My error message is 

[email address removed] has the file open in another copy of QuickBooks.

Close the company file in the other copy of QuickBooks. Then you can open it in this copy of QuickBooks.

Background info: I needed to erase my hard drive, and then I restored my mac with time machine. Looks like quickbooks still thinks my previous user account is using the company file, but that user account no longer exists. 

Please, please help!