Yes, it's possible for cats to be allergic to something in their litter. Normally this shows up as skin problems, but if your cat decided to taste the ground corn litter, then it could have caused irritation that resulted in diarrhea. One easy way to test this is to remove the new litter and replace it with what you used to use and see if the diarrhea clears up. If it does, then the corn litter was the most likely culpret. In that case, either get rid of the corn-based litter completely or put it somewhere where he can't get into it.
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