Hi T-Bear,
I guess you are using FPC 2.6.0. There is something problematic with that and GLScene. I installed FPC 2.4.4 and the Lazarus version with that (0.9.30.2 I guess) and GLScene was compiled and installed. Also, just today I have found this thread and this may hold the key for a successful FPC 2.6 based installation. I did not try it yet, but it was the errors I encountered if I recall correctly. (Go down on the thread though.)
http://lazarus.freepascal.org/index....c,14676.0.html
Hope this helps.
Anil
PS. Sorry for the probable mistakes, I'm not a native speaker.