Here at HQ we had a similar problem but I thought it came from our instance of Alfresco. Unfortunately we did not have time to really debug this, especially as it's not reported as an issue.
I don't think that Moodle would block the access to Alfresco, however your network administrator could check if a firewall or something disallow the connexion between them.
The error I got here is that after the login (which works even though it does not look like it), a SOAP exception is raised from the server.
WebDAV should work fine, there were a few issues closed recently in its regard.