Added releaseError page in revision 755173.
Yes, it's somewhat related.
This is just an improvement on how the errors are handled when build agent has been delete/disabled. So instead of getting a stack trace or not releasing at all without any message when the build agent is not available, I just added an actionError and redirect it to another page so users will be informed when something like that happens.
If you're going to write a selenium test, just disable/remove the build agent where the last build was performed and when you try to release, it should redirect you to the releaseError page.