Redownloaded the trainer 3 times and tried them, still same issue. I can use all other trainers made by 0x90 except AC3, even the non-steam version of the trainer I'm able to run without the error message (But will crash game when using, but I'm just testing to see if same issue is on other trainers contributed by 0x90).
The trainer itself extracted to be 1.04MB, if anyone can confirm that the file was not incomplete, I'll be greatful.
I'm going to reinstall net framework to see if it will resolve the problem.
to be perfectly honest, I would suggest trying to play through the game without it. I am an avid user of cheats, hacks, and loopholes, however with AC3 although getting 100% completition might be infuriating, it is all the more satisfying when you actually acomplish a mission. It should be noted however that AC3 is vulnerable to cheat engine and 4-byte searches as my 10 million pounds testify to . I have yet to try health, but i know it works on ammo and tools, and it seems the values are in the address range rather far down such as around the F-------- (- is meant as placeholder for address value, if you don't know what i mean try the cheat engine built in tutorial) region. hope this helps enjoy the game, happy for those that have a working trainer and my sympathy to those who don't.
In closing, if a trainer doesn't work, break out a hexadecimal editor