On one test I did, I was getting "Connection to remote server failed". The server was up as well as credentials, so I couldn't know what was happening.

This job is build #[1] on the remote server.
Triggering remote job now.
Connection to remote server failed, waiting for to retry - 10 seconds until next attempt.
Retry attempt #1 out of 5
[...]

At the end, I was adding parameters to a job that didn't have any. So /buildWithParameters replied with HTTP 500.
I'm requesting for adding details to the error above. This case is one that would be nice, but also authentication/access errors, etc.