Sharepoint UserGroup.asmx GetGroupCollectionFromUser(..) returns empty collection

Question

Hey

I try to get all the user groups that the current user is a member of, I am using the UserGroup.asmx GetGroupCollectionFromUser method.

However this method returns an empty collection even if the user belongs to some groups. I checked the user group settings that allows all the group members to see the membership to this group.

And the problem is not the writing the wrong username because if the username does not exists in the site collection it throws an exception.

Any idea what might be the reason?

Thanks a lot ...