Go into the games' folder, which will be in the steam folder..
C:\Program Files (x86)\Steam\steamapps\common\Borderlands 2\Binaries\Win32 (if you have a 64 bit Operating System)
C:\Program Files\Steam\steamapps\common\Borderlands 2\Binaries\Win32 (If you have a 32 bit OS)
There you will find borderlands2.exe right click on it and select properties, on the new window goto the details tab and it should show your current installed version there.
Match that up with the trainer in the list with the same version and away you go
If you have got the right one and it still crashes then you may have a slightly different version thats tied to your geological area, the best thing to do is to send in your borderlands2.exe for them to look at. Send to email@example.com with a suitable topic to the email of course and attached file (zipped or RAR'd up to minimize the size to send)
firewall and other security software.
on trainer and game.
version and distribution.
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