A Christian once very seriously explained to me why the very old song "Greensleeves" was a sac-religious source for a Christmas Carol ("What Child Is This")--because it was music written by Satan. - Seriously.
EDIT - July 18th: It's come to my attention that this true anecdote offended some Forum members, and that's unfortunate since I had no intention of offending anyone.
I also didn't intend for that funny little story to be a statement about any group of people as a whole. It popped in my head when I read Jeff's original post because it's an example of irrational, superstitious thinking, and the person in the story was passing on what he had been told in his own church.
To me there's a parallel between that and how The Church (which means the original organized Christian church, the Roman Catholic church) attempted control via censorship, preying on the superstitious bent of its congregations - ie: "You shall not have this particular kind of music in your churches because we deem it inappropriate, and to contradict us will imperil your soul."
--The rest of my original reply is below---
Interesting quest you're on, which will indeed need to take you beyond what you would find online. The Church has banned so many things over the centuries, not many of us would be surprised if this persistent story that some forms of music were banned at various times is true. But it will take some serious browsing in the dusty tomes of the larger libraries - Good research assistants at large libraries, perhaps those at universities, could help you out.
That sounds like a tough quest. Even today rock and roll and hip-hop aren't officially banned in many churches, but you probably won't hear it there. There's just so much tradition involved that isn't necessarily written in stone.
You might need the use of an academic library where you can view older texts and see if they list their sources. (Maybe Google books might have some stuff too.)
If historians 500 years from now write "Many churches in the 2000's did not allow hip-hop" they'd be right (unless I'm just unaware of the hip-hop churches), but I don't think we have any documents officially banning it...
Guess it also depends on what is implied by the word "ban" ... an official ban, or perhaps there was a more traditional unwritten ban, as there sort of is today.
I can't direct you to any medieval primary sources, but I can tell you that in the Middle Ages the Church was very particular about what sorts of music were allowed for liturgical use. Until the Renaissance, sacred music consisted almost entirely of plainchant and primitive polyphony, and most instrumental music was forbidden.
Things got much more interesting in the Renaissance, and during this time musicians within the Church were responsible for a tremendous growth and development of Western music, but by the mid-16th Century the hierarchy of the Church was becoming concerned about the cross-pollination of sacred and secular music, and that liturgical music was becoming too florid and complex. Some felt that composers were obscuring the sacred texts with dense and elaborate counterpoint, thereby making the music unsuitable for worship. Do some reading on the Council of Trent for more information on this. Legend has it that there was some sort of momentum to ban polyphony from the Mass entirely, but that G.P. da Palestrina swayed the Council by composing his Missa Papae Marcelli and demonstrating that beauty of composition and clarity of text were not mutually exclusive. Modern musicologists hold that there is no real evidence to support this, but it makes for a good story.
And Rosicrucians forbid the use of percussion instruments and vocalizations in their initiatic rituals. The exception being the gong which may be used to signify specific entrances and exits of the participants.
EDIT: I know you asked for actual documents - please check the post below this one - I'm pretty sure I can find something for you.
Medieval music "scholar" - yes, to some degree - by my own effort if not officially.
I will answer as best I can, but before I begin:
In light of the original post (not because he asked - that's the good part - but rather due to the controversial nature of the subject) and first comment, this thread could be borderline "Church Bashing" and I really feel I need to intervene at this point. Please think about members in the forum who may be part of a particular religion before you begin talking about who did what, when, where, and why. That applies to all religions.
I'll try to divide this into parts:
1. As to what particular forms of music the Catholic Church banned or prohibited has to do with the nature of the different types of music.
The "forms" - by which I'm guessing you mean genres or styles - that were not allowed were those of dance music. The Church wanted composers of the time to write music specifically for aiding in bringing out the glory of the mass and other celebrations. This music would have to be of a particular style to do that, and the "feel" of dance music was seen to be too distracting in nature to aid in bringing one to a more full understanding of the mass. I'll give an example, and then come back full circle to explain this in its original nature.
To avoid anyone poking fun: THIS IS AN EXAGGERATION to make the point clear. Please heed this and focus more on the point at large.
Say you are sitting in church waiting for service, mass, etc. to begin. You are either in quiet prayer, just sitting and taking in what's around you, or in light conversation with family or friends. All of a sudden a blast of techno music flies out of the speakers at 300 BPM with the most aggressive and undefined synthesizer lead you've ever heard. A man with a grungy voice begins to scream words that vaguely sound like, "JESUS!!!"
At this moment, I doubt anyone would be thinking about Jesus unless they planned on using His name as an expletive because they were scared to death. One's thoughts would most likely be on the how loud the volume level is, the awful sound coming from speakers, or they might just be in shock.
In the example, the music does not fit the liturgical venue - meaning that it distracts instead of attracts. The music that should have begun at that point would either aid in prayer and contemplation, or help to segway into the beginning of the service, letting everyone know it's time to begin.
That example, again, was an exaggeration, but I hope that I painted a clear picture of the importance of liturgical music being appropriate for its purpose.
2. Back to chant and dance forms. The musical scope of the time was not as large as it is today, so the difference between genres seemed greater. While we, in the modern era, can listen to anything from raging techno to Bach, the music that was experienced by the medievals only ranged from chant to dance music.
Chant and early polyphony were designed to make one more mindful of the current prayer/mass-part and help one understand the significance or meaning of what they were singing. Dance music was designed to aid a social gathering to build energy and give dancers a rythmic structure to rely on. The difference really is in the rythmn. Dance music has a consistent beat that does not wane to anything but musical interpretation - meaning it generally stays the same speed until key points - such as the end. Chant's rythmic structure, musical interpretation, and speed are all based on key words - meaning that the beat structure is not consistent - it is there to bring out important words in a line, pointing out significance.
This being said - neither of the two forms could fulfill the other's role very well at all.
Consider this: Dance music has a consistent beat pattern. Therefore, the stress pattern is generally the same, meaning that key words may not land on a stress due to the number of words in a line or other obvious complications without trucating the text (I can talk about this later). In addition - whenever a stress pattern repeats itself, or whenever anything in music repeats itself for that matter, the listener will "forget" about it. So even if key words are on the strong beats in whatever time signature, the listener will probably not find that of much significance because all songs of that nature have the same stress pattern - therefore meaning they've already "heard" it before.
In the same way: Chant is not very good dance music - this needs very little explanation. With the stresses and melody being ruled by the text, the beat pattern is not the same, and thus it will not serve well to aid dance - a heavily rythmic artform.
What's not said can be just as important as what is said. The medievals said dance music was not of a nature to aid in church, but the "gypsies" as they are called, never said that chant was any good for dance - the two forms serve different purposes.
I hope I have shed some light on your question and helped you understand this very difficult subject (I know first hand!) a little better,