Well here's one of the reponses I got from the nice people at GLScene:

The best is to use driver 6.5 again.
If you realy need last driver you can use the Viewer.free method in the
OnClose form and wait 7.0 driver.
I have talk a lot about this problem with ati people and I wait to see if it
is corrected.
Basically what my problem was that after reinstalling windows SP2, and then installing the latest graphics drivers, then installing Delphi Enterprise 7 and GLScene, whenever I closed an GLScene application in Delphi OR whenever I opened somebody elses GLScene application, I would get a context activation error and the application would freeze.

If it helps the graphics card im using is a PowerColour x850xt

If im honest I dont know who is really at fault for this error, but if it worked fine in the 6.5 drivers and works fine (I assume) for NVidia graphics cards, its possible something could have gone wrong in the 7.0 Drivers, but then again, i know nothing about hardware! Let me know if any more info would be useful