In my testing of the SCCM 2012 and the migration I accidentally deleted some of the computers that had been collected and was manageable and this is what had to be done to fix the problem. I was getting the error of “MP has rejected policy request from Client GUID: because the SMSID is marked as blocked. in the SMS_MP_CONTROL_MANAGER logs. I dug around and finally found that it had to do with the certs that was installed on the client. I had to go into the Certificate MMC for the computer and under the SMS folder delete those certs in there. Did a manual uninstall of the Client and then deleted the CCM folders from within the Windows folder and also the SMScfg.ini file after the uninstall and then reran the install and then the client picked back up and showed back up in the Management Area. I know a lot of work for a whoops but that was ok learned something new.
Til later just Roger