The server encountered an internal error or misconfiguration and was unable to complete your request.
If you were trying to attach a file (especially a build log), please verify that you have read permissions to that file. Browsers tend not to implement error handling, and instead submit a malformed request when they cannot read the file.
If this is the case, please use chmod or chown to ensure that your user can read the file, and try again. Most browsers support resubmitting the request without losing data through refreshing the page (F5 or Ctrl+R).
For more details, please see this Firefox bug report from 2008: Should give error message when file upload fails due to insufficient permissions .
Please contact the server administrator at webmaster@gentoo.org to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.