This article will cover all the facades of QuickBooks Server Busy Error, including the causes and the troubleshooting methods. Read More:

To fix QuickBooks Server Busy Error:

Close QuickBooks on all computers.
Open Task Manager, end all QB-related processes.
Rename the QBWUSER.ini file.
Disable QuickBooksDBXX and QBCFMonitorService in Services.
Update QuickBooks.
Restart the computer.
Open QuickBooks and check for the error. If the issue persists, seek professional assistance.

Regards,
Peter