The company could not be opened because the file COMPANY.DAT is missing or damaged.

I have a third party application that integrates with Sage 50. After a client has copied their sandbox company to a new file for their production company, I am no longer able to open the Sage 50 company and receive the following error:

 

I have seen instructions for other damaged DAT files, but none that refer to this file specifically. I can see that the recommendation is to restore the backup to a new company, however restoring a backup to the new production company is exactly what has caused this error in the first place. When we were just working with the sandbox it functioned normally. 

Do you have any suggestions about how to proceed?