If you do not yet have a registration code...DO NOT use GigaClean after installing GigaStudio 3.0.
As a part of its cleanup, it wipes out all registration values, everything. If you are running on a grace period, it will wipe that out, too.
This isn't a bug...it's the way GigaClean has to work to be effective. If someone could just re-start the grace period after running GigaClean, then obviously the security of the app would be thwarted.
If you are having a setup problem, GigaClean is very likely not going to solve it, anyway. It's like using a nuclear (or nucular for fans of President Nutjob) bomb to clean your desk. Much more likely would be something which is not yet set up correctly in preferences, etc.
DO use GigaClean to really clean your machine of 2.5x before you install, if you wish. That will not nuke your 3.0 registration or grace period. BUT even then, as I said before, you must have your 2.5 registration info if you ever wish to reinstall it. And if you run GigaClean after installing 3.0, you must also have your registration info--or you won't be able to get back into the grace period.