Internal Errors (handled in VaadinService#handleExceptionDuringRequest) are forwarded only to an ErrorHandler registrated at VaadinSession,
but MGNLUI-1140 was setting the VaadinSession-ErrorHandler to "null".
Because of that nobody is seeing the cause of "Internal Errors" (no stacktrace/message in log or Pulse).

Example: JBoss Application Server 5.1 has a Bug which is leading to Internal Errors starting with the second AdminCentral-Login (see attached stack trace). This stack trace was only visible with an VaadinSession-ErrorHandler.

Maybe you could registrate an AdmincentralErrorHandler for VaadinSession instead of setting it to "null"