This happened to me a few times with this trainer as well. I have the steam version of the game. The F4 key failed as well. I had to restart my computer for it to activate correctly. This seems to be an intermitant problem with the trainer.
Create a scan exclusion in your security software for the Work folder which is located here -> C:\Users\YourWindowsUserName\Cheathappens\
You might want to look up your security software's scan history/logs and quarantine and clear them and reboot your PC.
Delete trainer and all files in
Reboot PC to clear excess memory, get a fresh copy of latest trainer and
make sure trainer in is folder excluded from virus scans.
may need to be added to exclusions as well. Run trainer as admin and try again.