Can you provide the full stack trace? It will be logged in Admin > Errors.

You can set up a retention policy that will handle this feed cleanup.

I will also add that there is a feature in the pipeline named "Release Archiving", which will allow deployed releases to be archived and delete the artifacts from a release for all but deployed builds. It will also delete the execution logs and messages for non-deployed builds. This feature (at the moment) is not scheduled for any particular release, but it should be coming in one of the next few minor (3.X) releases.