SAP XI Demo - 500 Error

I have completed the XI installation on a single server and executed the steps in the XI Demo configuration guide. In executing the "Check Flight Seat Availability" scenario, after clicking "Check Availability" from the "Choose a Flight" screen I receive a "Unable to check flight availability" error with the Error Details stating a 500 Server error occurred. Checking the exchanged messages in SXMB_MONI I see an error returned indicating REQID not found.

I tried changing my INTEGRATION_DIRECTORY_HMI path prefix from /dir/cacheRefresh to /dir/hmi_cache_refresh_service/ext but get another even longer java execption error.

Any suggestions?