How can I troubleshoot Error 5100 MP287 related to firewall settings?

First, ensure QuickBooks is allowed through your firewall. Add QuickBooks.exe and QBW32.exe to the allowed programs list. Temporarily disabling your firewall (with caution and only for testing) can confirm if it's the root cause. If so, create specific firewall rules for QuickBooks to allow inbound and outbound connections on necessary ports.