Also make sure nothing is blocking the trainer.
It is also said that for some, the CCCP codec package helps.
Also bear in mind the trainer is linked to the version of the game, so 1.5 would be for the patched 1.5 Witcher.
As I said, I did try everything listed in the troubleshooting page. Nothing is blocking my trainer as I added it to all the exceptions lists and even tried disabling/uninstalling my anti-virus software. I just tried the CCCP codec pack to no avail, and as I said also, it is the correct version of the trainer since all others make the game crash and the Demo of 1.5 seems to work okay, not totally sure why just the demo and not the mega will work.
EDIT: I did a restart of my system and it appears to be working now.
[Edited by jharlan7581, 5/21/2011 11:39:19 AM]