Hi taylor,
Just a reminder about garrisoned units. Garrisoned units in your offensive line-up can sometimes lock up the combat simulator and your attack or simulation wont work. Remove any infantry units from their aircraft / vehicle and try again. If this is the problem, in future garrison your infantry at the last moment before your attack or simulation.
And never leave infantry units garrisoned permanently too, only garrison them into their vehicle / aircraft as required.
Also, the EA staff & developers for this game have previously stated they do not monitor or follow these forums and very few experienced players of C&C:TA (if any) come here too. You would do better posting all future problems/comments regarding Tiberium Alliances to the dedicated C&C:TA forums at: http://forum.alliances.commandandconquer.com/index.php