I was updating a site from MOSS 2007 -> MSS 2010 and I tried to access the site and kept getting a blank screen and the word "Done" in the bottom left hand corner of the screen.  So I looked in the IIS log and noticed that there were a lot of 401.1 and 401.2 entries in it.

 

So immediately thought of the LoopBack Test that used to happen in MOSS 2007 and sure enough after I added the appropriate Registry Key it all burst back into life !

 

In case you forgot what ths key is  - see Joel Olsen's blog -> http://blogs.msdn.com/joelo/archive/2007/06/14/i-m-indexing-and-i-only-get-errors.aspx

 

Just because it is MSS 2010 it does not mean that the old MOSS 2007 gotchas have gone away.