May cat is very, very fussy about the type of letter we use. She likes one that is soft on her feet and does not smell (we use a clay one now).

When we used a litter she didn't like walking in, she would poo anywhere and TOTALLY refuses to use her tray!

Try some sawdust even. We resorted to that until we found a litter she liked. It does smell a little more but is very, very soft on their tootsies.