500.19 error NetBios command limit thread on forums.iis.net
Here is a great thread on how a person reported fixing a problem 500.19 error NetBios command limit and using a UNC based content architecture.
http://forums.iis.net/p/1165964/1937935.aspx
http://support.microsoft.com/kb/813776
Check out the UNC tag regarding others that have great information.
http://weblogs.asp.net/steveschofield/archive/tags/UNC/default.aspx
Steve Schofield
Microsoft MVP - IIS