QuickBooks Server thinks that another copy of QuickBooks has modified the file. That would occur if the file were open in another copy of QuickBooks. All copies on QB on the network must connect through the server and not open the file themselves - only the server can open the file.
This can also happen if the file is being shared via iCloud, DropBox, Google Drive, etc and some other machine is modifying the file in their local copy.
Do either of those sound like the issue? If not let me know and I can request some log files from you to give to our engineers.
