The company file cannot be closed at this time because there is another application (LMN Quickbooks Sync) which is using it. Before you can close the company file you must either close that application or instruct that application to end its session with Quickbooks.
Sometimes Quickbooks will not close and it says that it cannot close because LMN is still using it, even though you have closed the LMN Sync Tool as well as LMN itself. This is most likely because the LMN Sync Tool is still running in the background (processes are still running). This is a simple fix.
Easy Fix: The easiest way to resolve this issue is to restart your computer.
Quick Fix: If you would like a quicker resolution and are familiar with using the Windows Task Manager (Ctrl+Alt+Delete), you can close the LMN Sync Tool there and it should resolve the issue. You can see an example of this method below: