nginx seems more stable (or something misconfigured for apache?)

try the following (rstudio-server-0.97.551-i386.deb, Ubuntu 12.04):
- user login to server configured with apache proxy
- on the server: sudo rstudio-server verify-installation
- user, when typing, receives “Error: Status code 503 returned”
- user “sign out” -> “Service temporarily unavailable” - unable to login!