Another question (sigh). There are 3 pairs of words starting with the same letters (Q, L and N). This tells us the positions of the 9 letter solutions beginning with L and N, and leaves 2 9 letter solutions. One of these is ONE GALLON (?), the other is BIRDCALLS (according to dannyk13, below). If the shorter Q solution is QUIRES (that's got to be right, no) then ONE GALLON can only go in the top right quadrant. That means that BIRDCALLS should go in the top left quadrant but it clashes with the 'U' in QUIRES.
Ok - I've got it now. I entered the two clues beginning with 'N' in the wrong place because I didn't pick up the error in the lengths of the B solutions. Many thanks for the replies.