Sometimes a conflict in the updated files can prevent the game from properly identifying your CD-key. Usually, refreshing your CD-key will resolve the issue. Note that this will only correct the error if you used the same Windows account to install, patch, and troubleshoot the game. If you have switched Windows accounts at any point it is recommended you uninstall, reinstall, and repatch using the same Windows login.
If you have Battlefield 2
Click Start.
Go to Run.
Type regedit and hit OK button.
Click on plus sign next to HKEY_LOCAL_MACHINE.
Click on plus sign next to SOFTWARE.
Double click on Electronic Arts folder.
Double click on EA Games folder.
Double click on Battlefield 2 folder.
Double click on ergc folder. NOTE I HAD TO CREATE THIS
Data displayed will probably have x9392 only.
Right click on it and select Modify.
Type in x9392 and then your CD key.
note: don’t include hyphens.

Example: x9392(your Battlefield 2 CD key here)
If you have Battlefield 2: Special Forces
Click Start.
Go to Run.
Type regedit and hit OK button.
Click on plus sign next to HKEY_LOCAL_MACHINE.
Click on plus sign next to SOFTWARE.
Double click on Electronic Arts folder.
Double click on EA Games folder.
Double click on Battlefield 2 folder.
Double click on ergc folder. NOTE I HAD TO CREATE THIS
Data displayed will probably have x9392 only.
Right click on it and select Modify.
Type in x9392 and then your Battlefield 2 CD key.
note: don’t include hyphens.
Double click on Battlefield 2 Special Forces folder.
Double click on ergc folder.
Data displayed will probably have x9392 only.
Right click on it and select Modify.
Type in x9392 and then your Battlefield 2 CD key.
note: don’t include hyphens.
note: do not use your Battlefield 2: Special Forces CD key.
Example: x9392(your Battlefield 2 CD key here)

If the issue persists, you will need to uninstall the game completely and then reinstall and repatch to completely remove and replace corrupted files.