OCS 2007 & SQL2005 SP3 – Pool backend discovery failed

A few weeks ago I was installing an OCS server in a lab environment for the purposes of giving demo’s and testing some stuff out myself.

However, before I could actually even start I ran into a nice little problem.
First I prepared the AD, as documented by Microsoft, no problem there at all. Then I launched the Create Enterprise Pool from the setup.exe

In the next screen of the simple wizard you need to provide a pool name, after which the FQDN is filled in automatically and the SQL backend. (if your SQL farm is separated by a firewall, make sure port 1433 is open from the OCS to the SQL)

That should be that. Unfortunately for me, I received this error:

Since I have a SQL 2005 server, I checked the Service Pack level and made sure it was the latest version (SP3). The Backward Compatibility pack installed on the OCS is from the same SP level. No problem there you would say. But no matter how I tried configuring the OCS pool, it didn’t work.

I guess not many people have this issue, since I didn’t find much online about it. But then I stumbled across this article from Microsoft: You cannot create the enterprise pool for Office Communications Server 2007 on a back-end server that has SQL 2005 Service Pack 3 (SP3) installed
Basically it says the backward compatibility pack from SP3 does NOT work correctly and what you need to do is this:
1. Uninstall the SQL 2005 SP3 Backward compatibility pack
2. Download the correct backward compatibility pack (SQLserver2005_BC.msi) from this link: SQLServer2005_BC.msi
3. Install this new BC pack

Immediately after that I tried the OCS enterprise pool wizard again (no reboot) and what do you know: it flew straight through!