I’ve gotten that GDI error before, when my computer was hanging during GK2 installation. I was able to get rid of it by quitting something that’s running on the task manager. I forget what it is but I’d know it if I saw it. Next time you get the error, can you do ctrl-alt-del and post everything that’s listed on the Processes tab? (Rebooting your computer also gets rid of it… or did in my case, anyway.)
I think the 999.pal error happens when you don’t have CD#1 in the drive when you launch your game. This is another problem I had with GK2. Putting CD#1 in the drive fixed it. (I was able to keep CD#1 in one drive and use the other drive for whichever CD I was up to in the game, and this worked fine.)