Two factors, sheer complexity of the Warscape engine, SEGA putting a knife to CA's throat to release this game long before it was completed.
1st. Make sure your game and the trainer match!
2nd. Make sure your security programs are ignoring the trainer or turned off.
3rd. Read and follow the trainer instructions to the letter.
4th. Do not run any mods that will change any part of the game that the trainer use's or the trainer will not work at all!
5th. Run the trainer and steam in admin mode.
Oh and do not use beta patches.