Cascading dropdown lists and error 401

Until recently we successfully used the tip from Ishai Sagi on cascading lists, but suddenly our users reported getting a error when trying to use the drill down Master-Detail dropdown lists.

Looking at the IIS log we discovered the call to owssrv.dll was done anonymous and resulted in an error 401. With good help from a consultant from Key2Know we found that the issue was related to a loopback check security update on Windows Server 2003 SP1. The solution was found on http://support.microsoft.com/kb/896861 where you can read more about this issue.

We implemented solution 1 on our Web Front Ends and this resolved the issue.