If you are able to start the game but not load saves it's possible that the problem is your installation directory. Please make sure that the folder where game is installed does not contain any special characters. For example, this will not work:
G:\Chris's games\Steam\steamapps\common\BATTLETECH\BattleTech_Data\Managed\UnityEngine.dll
In the case above, the ' is causing Unity problems. Simply remove it and you will be golden.