This was first reported when customers installed the OFP Ultimate Upgrade 4 patch. Initially BIS attributed this to be caused by players not downloading and installing the same version's separate standalone server file.
So first make sure the the standalone server program is the same version as the OFP version you've upgraded to. If you're not sure, you can verify the server EXE file's version number using Windows Explorer.
Next, make sure that the server EXE file is located in OFP's base directory and nowhere else.
If you still receive this error after verifying the sever EXE file's version number and location, you should contact BIS support about it. In the meantime, you can tentatively bypass the problem by running OFP's main game executable program, OPERATIONFLASHPOINT.EXE, with the -server argument and with the original CD in the CD drive.