Assembly load failure installing the 2.0 Framework

I just helped debug an interesting framework failure.

Product: Microsoft .NET Framework 2.0 -- Error 25015.Failed to install assembly 'C:\WINNT\Microsoft.NET\Framework\v2.0.50727\Microsoft.VisualBasic.Vsa.dll' because of system error: 0x80131107

Turns out the customer had their COMPLUS_VERSION envionrment variable set to 1.1.4322 (the 1.1 framework). This caused mscoree.dll to load the 1.1 version of framework and use that to GAC the 2.0 assemblies. 

The workaround is to delete that environment variable and rerun the install.