By default the Assigned To list comes from the members of the Team Project group called "Contributors". If you right-click the Team Project, choose Team Project Settings and then Group Membership and check the members of the Contributors group. If you can't see it in there try using TFSSecurity.exe:
C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE>tfssecurity /imx
n:"[TeamProjectName]\Contributors" /server:ServerNameOrUrl
Regards,
William D. Bartholomew (Team System MVP)
William D. Bartholomew
2009-05-10 04:06:10