Recover registered servers in SQL Server Management Studio 2012
If your RegSrvr.xml contains a  "password=....;" in &lt;RegisteredServers:ConnectionStringWithEncryptedPassword&gt; section, replace ";uid=...;password=...;" with ";trusted_connection=true;"

In the same file, replace:

&lt;RegisteredServers:CredentialPersistenceType type="CredentialPersistenceType"&gt;PersistLoginNameAndPassword&lt;/RegisteredServers:CredentialPersistenceType&gt;


with:

&lt;RegisteredServers:CredentialPersistenceType type="CredentialPersistenceType"&gt;PersistLoginName&lt;/RegisteredServers:CredentialPersistenceType&gt;


Now the server registration will try to use Windows Authentication.  Once the Registered Servers are loaded, you can go back and edit the registrations to use your SQL Authentication information.