Domino Webaccess related unusual problem

Hi Everyone, We are facing a typical problem with one of our web access user over IE 6.0 .Actually the user is under a OU Marketing and there is a common id called marketing .Whenever the marketing id is launchedin the URl as :

http://servername.domainname.com the login page appears and the credentials are given as marketing and password as say abcde then the redirection is changed to a user nsf say Paul Davis and the users in the marketing id cannot login with the marketing credentials ,however if we give the full path name say :

http://servername.domainname/mail/marketing.nsf we can get the login page and putting the user name and password for marketing can easily log in .At the same time the user called say Paul Davis who is mentioned has no trouble in accessing mail either from Notes Client or Web client .

What could be the problem.

We are on Domino 6.5.3 on Win-2003.

Ay suggestions are welcome .

Regards & Thanks,

Deep