I have recently experienced some difficulties with KGFF and KotOR Tool, and I have found that it comes from the renaming of kgff to GFFEditor.exe. However, this is not the software's fault, it is my OS's, specifically the XP registry, that is to blame (or the end-user, that idiot at the keyboard, uh, oh, me).
My solution, is simple and free and obvious - cCleaner. Cleaned up some registry keys that had programs pointing to renamed progs (that I had assigned through Properties prior to renaming, which is where I went wrong mostlikely), letting cCleaner delete them.
Reloaded the problematic files with GFFEditor(KGFF) and it was all good.
Lesson for those like me who got frustrated for a minute with the tools -
1. You can always uninstall and reinstall KotOR Tool.
2. If you are going to rename KGFF to GFFEditor, do it first before setting program associations for opening GFF filetypes.
3. If you botch the above, or are having problems, cCleaner is your friend (make backups)
Thanks again to tk102 for this tool, and all of your modding tools! I would be lost without them