I got the following error when I clicked "Downgrade to XXX" buton.

404 Not Found

Stapler processed this HTTP request as follows, but couldn't find the resource to consume the request

-> evaluate(<hudson.model.Hudson@64df80ff> :hudson.model.Hudson,"/updateCenter/plugin/updateCenter")
-> evaluate(((StaplerProxy)<hudson.model.Hudson@64df80ff>).getTarget(),"/updateCenter/plugin/updateCenter")
-> evaluate(<hudson.model.Hudson@64df80ff>.getUpdateCenter(),"/plugin/updateCenter")
-> evaluate(<hudson.model.UpdateCenter@54dfd702> :hudson.model.UpdateCenter,"/plugin/updateCenter")
-> evaluate(<hudson.model.UpdateCenter@54dfd702>.getPlugin("updateCenter"),"")
-> unexpected null!

If this 404 is unexpected, double check the last part of the trace to see if it should have evaluated to null.