ITunes error message: "We could not complete your iTunes store request. An unknown error occurred (4002). Any suggestions for curing this?
Perfect - thanks so much!
For anyone else wondering, the clue was in what was displayed on the screen after I turned iTunes Match on again: it asked whether I wanted to add this computer. Having copied my iTunes library over from the old machine, I'd completely forgotten that iTunes Match identifies each computer uniquely (not each iTunes Library), so was never going to work with this one until I specifically added it. Sorted!