Another quote from http://www.petsage.com/art_litter.htm

· Recognize that if your cat has had a bout of FUS, he may view the litter box as the cause of the pain. You may need to change the box, litter or location before he's "comfortable" again.

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*PIF Words*
Try changing brand new litter tray, with new 'gentle on the paws' litter, try fine sand, in a new location to disasociate with the previous pain of using the tray.
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