If this error occurs when you are importing an estimate to QuickBooks:
According to Google this means that the entity was updated using the Quickbooks GUI (ie manually) or through some other process immediately before you tried the import. Did you switch over to QB and edit something with LMN Sync Open?
If you saved everything in QB and then re-started it (being careful not to touch anything), and then ran the sync, it would work. If you have a networked database, you should also make sure no one else had QB open on a different pc, etc.