Well the tool was "refreshed" last year - as reported in this thread NEW VERSION - xONEx Online Booking Tool - FlyerTalk Forums, starting at post #16
While the user interface changed, it appears that the backend processing is unchanged - and is still giving errors

I too have been playing with the tool recently, and have been receiving the following well-know error messages:

When pressing the "Choose Flights" button on the first screen, I sometimes get:

• the "Up to 120 seconds" box, and then that box disappears and returns me back to the itinerary-building page without any error message or information as to why it didn't offer me flight options.
• the "Sorry, we've noticed that an error has occurred. The fastest way to get a quote is to contact [insert airline of first segment] "

When specifying two visits to Europe Middle/East (in conjunction with travel to Africa), I'm getting:

• Your itinerary cannot include any flown or surface sector between Europe and the Middle East. Choose another route and update your itinerary.
• One journey to the Middle East must be a transfer without stopover (ie less than 24 hours) between Africa and the previous/next continent. Please select another flight.

And I also got this new one:

• Your trip may include two stopovers over 24 hours in the continent where your journey started. If your itinerary includes both of these in your country of origin, one must be outbound and the other inbound. Additional stopovers under 24 hours are permitted in your itinerary. Please select a different date or flight