When GTK radiant stops working it's time to move all your mod folders, baseq3 configs, textures, shaders, custom models, and maps to another folder and delete quake 3. After that delete the GTK radiant folder (if it is not inside the q3 folder that is) and reinstall everything, this will only take about 15 minutes and it has allways fixed any problems I have had with radiant.
I put the new in b.