thanks to all for walking me through it. I managed to solve it last evening using the hint about the locked ones and then mostly a slow grind using hidden pairs to finally get to the solution and then to sleep!
tso: I do have one question when I was reviewing the help which stated "-- Now there is a naked pair of [23] in box 7, eliminating 2 and 3 from r8c3, bringing us to here:".
I know I must be missing something obvious here, but I looked at box 7 and saw 23,238,1238 and couldn't see how to actually eliminate the 23 as a hidden pair when following your excellent solution. Can you help me understand it? (Like I say, I must be missing something basic).
EHoward