Cura Engine not slicing...

Hi yo'all. I have had this occur a few times now and am frustrated as no understanding what has gone wrong..................

Loading an object to print in Matter Control MC using Cura seems to work quickly,smoothly - when it works. A number of times when I have started slicing after a typically normal time delay the MC resets the slicing and goes back back to the start but with no explanation why it cannot slice yet it will Slice in Repetier no issue. There is no 'cancelled' or 'failed' notice - just a reset. Is there a log or report somewhere that may tell me what the issue is/might be or a fix?
thanks
Rick