When I typed "mydomain\myusername" and clicked ok, it resolved it to "MyLName, MyFname (myorg/mydept) (myusername@myorg.com)"
Then after I click ok, I get the message pop-up I mentioned before.
Should the AD be setup in any particular way for my account to be added to this group? Could this error be generated if my account doesn't have the prereq settings that the TFSService account has?
I also experience this error. Trying to add project members from outside the primary domain. The check name finds the name, but when adding back to the member list, returns Couldn't add user/group, ... It may be in an incorrect domain.
That... I am not sure either... Does the OPS tree and Users tree have trusts set up... My guess is that you are in the same domain, but maybe there may be different trusts going on between trees.