It's a very easy fix.
Use one of the multiple CA cleaners available, then follow the intructions below.
1) go into your CA folder
2) go into your hs folder
3) go into your Update folder
4) double click on autoup, and manually update your hs files
5) go back into the hs folder, and double click on HSUpdate, at the top
6) try CA, it should not give you that error again
PS: This error may also come up, if don't have the latest patch. ( to make sure you have the latest patch, double click on the Combatarms_direct.exe in your CA folder. If it patches, good, if it just lets you play, then your already up to date)
If none of that works, do as Obama mentioned, uninstall, then reinstal your CA files/game files.