Easier errored msg recovery

https://github.com/daptiv/Ppm/pull/2516 has all the links

- [ ] @bearley please review
- [ ] @creg please review

- [ ] [tests pass](https://ci.appveyor.com/project/DrewBurlingame/daptiv-bus/history)
- [ ] [ppm tests pass](http://teamcity.hq.daptiv.com/project.html?projectId=PpmFeatureBranches&tab=projectOverview&branch_PpmFeatureBranches=74465-hotfix-errored-messages)
Maybe "specified message not found"? The message itself isn't invalid.