This code obviously doesn't need it, but I will in the program I'm writing. I've just made a test program to separate the error with the minimal code needed to reproduce it.
Of course in the final code there will be some procesing, but I'm happy that I haven't written 100 lines of code in a much more complicated program to debug this stupid error there.
And I've already written that I've tryed bookmark+first to eliminate this, but probably it's not this. Also I've tryed now [icode=delphi]if dataset.recno>dataset.recordcount-3 then exit;[/icode] after the 1st line with the exit, everything is the same. But I don't even reach the end of the dataset, because the dbgrid is too small to draw it (I know this by the logging line), so it really can't be this.

Also a new thing I've noticed that if I make a breakpoint then I see that this code runs for some time without error, and then never runs when the errors come.