Hello @rajendar erabathini ,
This normally happens when one of the existing accounts in the security group has a problem with it, e.g. it no longer exists.
From the SQL management studio, connect to Analysis services and go to Roles, under the roles, the user that has been removed from active directory will appear in question marks "?" , remove the user and reprocess the model.
Hope this helps. Do let us know if you any further queries.
------------
Please don’t forget to Accept Answer
and Up-Vote
wherever the information provided helps you, this can be beneficial to other community members.