title: Unreadable Data (CannotResolveClassException) in Jenkins
body: <p>I'm using Jenkins 1.646. I keep getting Unreadable Data entries in the Manage Old Data section. </p>
  
  <p><a href="https://i.stack.imgur.com/Dphiz.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Dphiz.jpg" alt="enter image description here"></a></p>
  
  <p>These entries appear for pretty much every build that occurs on my Freestyle projects. The builds complete just fine. Does anyone have any idea what I need to do to correct this? I did install the Pipeline plugin recently, and it installed a dozen or so other plugins with it, so my guess is that something is incompatible with my version of jenkins and / or another plugin I have installed.</p>