Comment 2 for bug 1049537

This second or third time I see this error, I had a look at it ~2-3 weeks ago, and that time it was faulty check in the code - it downloads always the latest version of jenkins.war, but checks against size of currently installed version, so after some time, you're bound to get this error.

I'm not sure it's the same right now (well, error doesn't give enough details), there obviously can be other errors (network access for example), so both issues (error reporting and short-sighted checks) should be fixed.