If Quickbooks is running on a Microsoft Windows Server and the server is an Active Directory server, then do the following:

Login as a Domain Administrator

Create a text file on the desktop called fixquickbooks

Copy this information between the equals section below and paste it into that file

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REM This needs to run in the server or there is a DNS conflict that causes the Network Diagnostics to fail.

netsh int ipv4 add excludedportrange protocol=udp startport=55368 numberofports=5

net stop "DNS Server"
net stop "QuickBooksDB28"
net start "QuickBooksDB28"
net start "DNS Server"

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Now in Notepad, when the file is opened, Choose File, Save as

Again, save the file to the desktop but this time in the filename type the following exactly:

"fixquickbooks.bat"

Save

Don't forget the quotation marks as part of the filename. 

This will make a batch file.

Now, right-click the batch file and run as administrator.

Now, go to any computer on the network or directly on the server and run Quickbooks and it is fixed until it happens again.  From now on, just right click the fixquickbooks.bat file (looks like it has gears on the icon) and Run As Administrator.  People will forget to run as administrator, so you might rename the batch file from fixquickbooks.bat to "Right-Click and run as Administrator-fixquickbooks.bat" to help you remember.

The reason you have to do this is because Microsoft DNS Server can sometimes use the UDP ports 55368, 55369, 55370, 55371, 55372 and Quickbooks needs those ports.

The symptoms are that even when you run Quickbooks Database Manager and scan the folder for quickbooks databases, the Network Diagnostics Failed message comes up and leads you to believe that there is a firewall issue.  This problem has been around since before 2008 and still happens today 13 years later.

Your welcome again Intuit,

cyanohydrax