I've come across a similar issue which I have found is caused by changes in the security of Windows 2008 (specifically the API calls used to perform domain lookups). Given the time that this was posted I am guessing that you could be using Windows 2008.

The scenario I found is documented in my blog.

http://matticus-au.blogspot.com/2009/08/windows-2008-and-xplogininfo.html

Matt