Accessing WebDynPro - Login Failed

Hi

Facing the Login failed error , though the User exist in SRM-MDM-Catalog Repository while Using the URL http://..MDM SERVER Host../ webdynpro/dispatcher/sap.com/tc~mdmsrmui/MDM_SRM_UI_App.

When it promps Server, after entering the server name ,under the Login Repository pops ups in drop down box,, then if we try to login.. getting an error "Login failed"

Pls let me know any other settings....