Problem is assigning TFS tasks for project contributors

Hello Everyone,

I have added some users into  FS project collection valid users.
and also removed some users from the group.
These changes are applied correctly for version control.
But these changes are not propagated into TFS tasks.
All the removed users are still appearing in the dropdown of TFS tasks and new users are also not showing up.
No clue about this.
And from the user side they could not connect to the TFS tasks in the TFS web access.
They get an below error.
"TF201072 a user or group could not be found. verify that users and groups used in your work item type definition have been added to TFS".
kindly someone help me on this.


Regards,
Arun.