Microsoft has just released the following KB Article:
Registration for an existing client is unsuccessful on System Center 2012 Configuration Manager SP2 and System Center 2012 R2 Configuration Manager SP1
Symptoms
The registration process for an existing client is unsuccessful on Microsoft System Center 2012 R2 Configuration Manager SP1 and System Center 2012 Configuration Manager SP2 when the client is reinstalled. This occurs when the client computer is reimaged or when the client is uninstalled and then reinstalled. The same symptom may occur when any changes are made to the client record in the ClientKeyData table For example, this symptom may occur after a move from a self-signed certificate to a public key infrastructure (PKI) certificate or vice versa.
When this issue occurs, errors that resemble the following are recorded in the Ddm.log file on the site server when the server processes the client registration record:
Microsoft SQL Server reported SQL message 8169, severity 16: [42000][8169][Microsoft][SQL Server Native Client 11.0][SQL Server]Conversion failed when converting from a character string to uniqueidentifier. : SMSDBMON_ClientKeyData_PfxCertsClientKeyData_Chg_upd