I’m fairly certain Umbraco does not produce that kind of error message.
Without any further details than that you’re experience 503 error, helping you might be too difficult.
See this section on how to ask a good question:
A guess would be that Umbraco has crashed, your page or a component on that page has an issue.
It could be a loadbalancer, proxy or other server that sits in front of Umbraco.
But without further details, we would only be shooting blind guesses at your problem.