win7 ultimate here, and i run my GC via steam. It works fine
Here's some details about the trainer (based on my personal experience):
1. The music MUST BE OFF (or it will crash 100%)
2. When you start your PC and login to GC, the trainer is defected sometimes, restart your GC and try again. It might need more than 2 attempt.
3. CONNECTION DOES MATTER
Believe it or not i can't start my trainer when 500-1k ping or when i downloading.
4. PC speed DOES MATTER
One time when my PC is running slow (after nonstop for about 12-24 hours) I can't get the trainer to work. So i turn off my PC for about 3-4 hours and i do the 2nd login attempt, it works flawlessly.
5. Test drive your trainer in normal dungeon not HD/event/LoJ
It's questionable but i have several cases like this
6. Lower your graphic might help
It doesn't matter in my case though, i can do the highest or the lowest the trainer still works.
7. Bypasser is not needed (except you want to run along with mod)
Good luck