if your on steam you should be using the latest Trainer or Editior and really the same for retail as you should be keeping your games up to date.
But to help your issue. Find where your steam folder is and follow below if you have installed xcom in steam.
In there find the XComGame.exe then right Click on it and click on the Details Tab and you should have something like this shown in the link below.
You will also need to tell your Security programs to ignore the trainer or turn them off completely! While running steam in Admin mode.
[Edited by ServiusTheBear, 8/19/2013 3:33:39 AM]