I suggest you to try
* Disable UAC
* Trying another injector.
* Running a Combat Arms cleaner to delete files from the combat arms folder you dont need.
* Turning off the Firewall and Anti-Virus programs.
* Try to Run CA from from the website or from the Combat Arms folder(CombatArms_Direct.exe)
* Make sure you have the latest directx: Download DirectX 9.0c (full package) - the latest version of Direct X
* Download NetFrameWork 4.0 if you dont already have it installed: Download details: Microsoft .NET Framework 4 (Web Installer)
And if none of the above works, reinstall ca.