Thanks for the replies chaps. In my original post I did not know it this problem was being caused by the data, hence my grievance. It took me some time to investigate the error myself and trace it to a repeatable failure with the data for 26 December 2016, although I could not see what it was in the Betfair source data that was causing the problem, and I don't think we have visibility of the Welldone database..?
That said, I would not agree that the application works perfectly as there is clearly something amiss in the data validation / error handling routines because the application does not handle data errors well. I would expect the application to at least stay live, and perhaps report the errors either in one of the logs and/or as a pop up message, rather than crash with an unhandled exception. I don't think I'm being unreasonable in this.
RE free data - the data are not free in my opinion. They are free directly from the Betfair site, but X-Feeder requires use of Time Machine, which seems to use a Welldone database that is populated with Betfair data (presumably from live data collection). As far as I am aware, one cannot retrospectively process the historic data without paying for Time Machine, therefore there is a cost.
Anyway, thanks for confirming that there was a data error that caused this. Happy new year everyone - hope it goes well.