Thanks all, my apologies. You are quite right I had failed to notice that the developer that had just worked was Microphen and not Xtol
I have been using Xtol for at least 2-3 years now and in winebags have certainly got about a year out of it after which I had used it all up.
I must admit that after seeing all the stuff on "sudden death" I did check on it after about 8 months with ath's test which is always sensible to do anyway.
My condolences to the OP. It is a swine when this kind of thing happens