Today while doing some vanilla BizTalk 2006 R2 installs, discovered the installer was choking with:

Error 5003.Regsvcs failed for assembly C:\Program Files\Microsoft BizTalk Server 2006\Microsoft.BizTalk.Deployment.dll. Return code 1.

Awesome. Other cases of a malfunctioning regsvcs executable have been reported. For reasons that remain unknown to me regsvcs.exe stop functioning following the installation of SP1 for VS.NET 2005 and the .NET 2.0. regsvscs.exe appeared to be intact, but invoking any of it functionality (including listing its command line help) would return nothing—hence the return code 1 problem.

Solution: Repair the .NET Framework 2.0 binaries. I grabbed a fresh copy of the service pack. It is important that egsvcs.exe functions correctly—you can test it while reinstalling the service pack by running regsvcs.exe /?. If it lists out help you’re good to go.