I am trying to add user(s) to an existing group via the function AddUserCollectionToGroup() of webservice "Users and Groups" (Web Reference: http:///_vti_bin/usergroup.asmx).
I call this webservice to add a user who is 'Local Administrator of SharePoint server' to a group and get SoapServerException with inner exception message as 'The user does not exist or is not unique'. But when I check for the users present in the site collection level, this user does exist.
When I try to add other user, say farm admin which is in AD, then it is successfully added.
Am I missing something? Any help would be appreciated.
(I am using Sharepoint Enterprise)
Thanks and Regards