|There was an error adding, modifying or deleting because it is already in use. QuickBooks error message: The transaction could not be locked. It is in use by another user.|
This error occurs when the transaction that you wish to modify in QuickBooks is already in use by another user, or the QuickBooks database has temporarily locked the transaction for editing or update.
Request that all users in QuickBooks complete their editing, and then sync again.
If you still receive the error, switch the company file to single-user mode, close QuickBooks, and sync again.