If you enter in URL that points to an action that does not exist (e.g. secure/project/ViewProect.jspa) you get a strange page with:

"HTTP Status 404 - Could not execute action [ViewProect]:Action 'ViewProect' not found or could not be initialized a class with that name could"

I think you should get a 500 page instead of this random and badly formatted error message. A 500 page is displayed if you put in a bad command name (e.g. jira/secure/project/ViewProject!dhdhdh.jspa).