Catkin is not alone in being unable to start populating the grid. Until I realised yesterday that an earlier post here about the space in 1a meant that the solution was a 3-letter word, not 4, I couldn't fit anything in either. Making steady progress now that I've ignored the maths element, but I'm confused as to which type of clue 29a is. My rapper without his title, plus a 'w', seems to work perfectly without any modification, although I wanted to use the 'd' from the message there.