QuickBooks Multi-user Mode Not Working is a very intriguing problem that needs to be fixed. You will have to pick the solution that fits the situation. Here are some common solutions that can be opted by you.
You can try fixing the issue by simply renaming the .TLG and .ND files on your desktop.
Also, you can also try to use the Quickbooks Database Server Manager.
Then another solution for this issue is to check the services on your server.
Try to configure the Windows Firewall settings on your desktop.
You may also Read - How to fix QuickBooks Error TD500