A recently deployed web service (IIS on Server 2008) was producing a YSOD with the error:
Unable to generate a temporary class (result=1)
Some cursory duckduckgo-ing suggested that the problem was a lack of permissions, for the user that IIS was running as, on the C:\Windows\Temp folder.
I compared the rights for that folder on the broken server with a working one, and the (local) IIS_IUSRS group had “special permissions”. Specifically, the right to “List folder / read data”.
Once that was set up, IIS was back in business. I presume this is something normally set up during IIS install, which either went wrong or was later corrupted.
Look on my works, ye Mighty, and despair! 