Something strange happened. I had to do some shopping, so I shut the computer down (with Windows process). After I came back, I reloaded the Sonar project file, in which the Strad/KP is assigned to solo violin.
Sonar loaded all KP/GPO older libraries and notified me that for KP2 a lot (I saw a long list) of files couldn't be found. I did a manual loading and it did load the instrument files, but in the browser there wasn't such thing as instrument. I just saw that the convolution scripts (etc.) were not present.
Did this three times, all occurences the same effect. In the main window there wasn't such thing as that brown violin color. Just everything stayed grey/blue-ish. This was also the case with the free-standing version of Strad.
After having re-installed The Strad I am back to normal. But still it is strange.