I have the latest version of the trainer and I am using Windows 10 and it works fine on my end.
Run as administrator
You patched the game to 1.07 AND got the latest trainer of July 18?
Other than that, maybe delete any/all trainers you have for it and dload the trainer again, and as said above, disable or make exceptions with A/V and firewall, Right-click and run the trainer As Admin.
I use the current trainer with the GOG version of W3 and it's working great.
[Edited by element5, 8/4/2015 3:08:21 AM]