Strange, it should take:
$WINDOWSDIR\Microsoft.Net\Framework\v2.0.50215
What was the error you got? My setup uses some registry values to get the latest framework version (v2.0.50215 in your case) so the other directory shouldn't be used...
The regasm.exe is always in a subfolder in the folder framework, so it isn't because of your 2 version... I'll talk to you at msn about this later today, it is interesting