Empire: Total War Message Board  

Then your anti-virus definitions updated and the trainer or folder it is in has to be added to the EXCLUSION list

Please disable/uninstall all antivirus, firewall and other security software including browser addons and extensions. Right click "Run as Administrator" on trainer and game. Please note that some security products may still block access to trainer injection even when disabled and must be completely uninstalled. If this is the case, please contact the product vendor for instruction on the proper way to prevent the trainers from being blocked by their software or find a better alternative.

or

Extract trainer and make sure trainer/launcher/editor is in a folder excluded from virus scans. Empty quarantine folder if needed or set anything trainer related (paths and EXE's) to ALLOW. Disable any Live/Active/Real-Time tools which may trigger false positives in security software that may terminate the game/trainer when it's activated or options used.

C:\Users\USERNAMEHERE\Cheathappens

may need to be added to exclusions as well. Click and select "Run as Administrator", read the instructions and try again.

Working fine for a few moths, but, now it's back to opening as a .tmp file, and, none of the solutions originally suggested are working anymore.