Updated 1/8/2015 - See bottom for instructions for newer operating systems.
After running VM Pro on a Windows 2003 domain controller (running Microsoft DNS) fine for 6 months, VM Pro decided to stop communicating with the IPO after a reboot. It looked like everything was fine as I could load the VM Pro admin interface, but obviously there was no communication between the IPO and VMPRO. This is because MS DNS decided to eat the ports needed by the VM PRO to communicate with the IPO (UDP 50791-50801)...
If you experience Voicemail Pro Not Operational, but it seems fine... and you get this in Monitor:
Microsoft DNS will fight for ephemeral UDP ports with DNS. One way to test this is to shutdown the MS DNS server, restart VM Pro and then restart MS DNS. If THEN your server is working you need to reserve the IP office ports so Microsoft DNS can't grab them:
Instructions for 2003 and 2003 R2 server:
Start Registry Editor (Regedit.exe).
Locate and then click the following registry subkey:
On the Edit menu, point to New, and then click Multi-string Value. There may be an entry already there, just modify it.
Right-click the new value, click Rename, type ReservedPorts, and then press ENTER.
Double-click the ReservedPorts value, type the range of ports that you want to reserve, and then click OK.
Quit Registry Editor.
Restart your voicemail pro system (full reboot)... now your MS DNS will not try to grab ports that VM PRO needs to operate.
Instructions for 2008 and 2008 R2 server:
Server 2008 and 2008 R2 do not support the above registry entry. You will need to download the following hotfix from Microsoft, install it, reboot and then run the command below.