When attempting to add members to a group the approval by primary owner built in workflow does not get sent to the approvers listed in the approval rule.
The following error is logged in the event viewer:
Your changes cannot be applied. The operation requiesting the changes requires approval, but the system fialed to determine the persons authorized to approve this operation. This problem may occur due to inconsistencies in directory data the approval rules rely upon, or because of incorrect configuration of approval rules. Please contact your system administrator to verify that the approval rules are properly configured.
Check the built in workflow Approval by Primary Owner to confirm the Approval Rule is setup with the correct designated approvers.
Confirm the group membership is able to be completed.