ArcGIS for Desktop 10.1 - WCS Services and ArcGIS Server 9.3.1

Many users with ArcGIS Desktop 10.1 are unable to connect to a WCS Service served through our ArcGIS Server 9.3.1 on Windows Server 2003.
The service is added to the GIS servers list but when the user try to add to the map there is the following error:
"Could not add the specified data object to the map. Failed to open raster dataset".
Also the WCS Coverage properties is without informations.
With one user i investigate the problem using fiddler and inspecting the requests and i note that ArcMap sends a WWW-Authenticate NTLM Header and the server Respond with HTTP/1.1 401 Unauthorized
The service works well with ArcGIS desktop 9.3.1 and 10.0.

The WCS Service is published at: http://map.sitr.regione.sicilia.it/A...rver/WCSServer

Someone have the same issue?

Thanks, Agostino.