It is a rather generic error message that can occur for a number of reasons. Further details are needed to pinpoint an exact cause. Do you know if your user can submit now? There was service outage earlier this week that may have caused the problem. Other issues are browser security settings, company or individual firewall setting, or actual bugs to out product. If you could get more information from your user such as their Operating System and version, browser version, if the error is still occuring, when the error occurred that would be helpful.
Some things your user can try in the mean time is clearing their browser cache, restarting their browser or trying a different browser.
Software Quality Engineer
Adobe Systems, Inc.