AVG falsely reports that carrier.exe is infected, and blocks it from running. If you use AVG, the following method will solve this problem:
1. Just in case your copy has become infected, try uploading the file to virustotal.
2. if the file is clean, add it to the AVG Resident Shield exceptions.
Open the AVG interface, look in the Tools -> Advanced Settings.
navigate the tree to Anti-Virus -> Resident Shield -> Exceptions.
add Carrier.exe to the list (default location c:\program files\bohemia interactive\carrier command gaea mission\carrier.exe)
3. this will prevent AVG blocking access to the file and allow you to run the game normally.