Cloud Control Error EM-04050 when trying to upgrade a plugin...

I was recently asked to update the EBS Plugin from to in my Cloud Control 12 setup. During the prereq steps I got an error: "EM-04050: The selected plug-ins cannot be deployed on the Management Server because there are some Management Agents on which incompatible versions of these plug-ins have been deployed."
Unfortunately no other information was given. I knew there must be some old versions of the Agent plugin floating around out there but didn't have an easy way to find them. Oracle Support to the rescue... Run the following against your SYSMAN schema:

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