There are many reasons that cause Quickbooks database server manager network diagnostics failed, the very common reason is disabled Quickbooks database service. When Quickbooks database server manager is outdated this is one of the reasons, if windows firewall is blocking Quickbooks from accessing the required ports. To solve this error you can use the Quickbooks file doctor tool, you can update the Quickbooks database server manager and resolve that error, by configuring windows firewall you can solve this error, etc.