In college I had a cat who ate the tape in one of XTC cassettes (it was "Skylarking" for anyone who cares.) We didn't know he'd done until what looked like black tapeworms starting oozing out of his butt. (Sorry to gross anyone out.) We rushed him to the vet, and the vet said we were lucky because the tape hadn't wrapped itself around any organs or otherwise created an obstruction. So the tape itself obviously wasn't toxic to him. I'm sorry about this kitty who appears hasn't been so lucky.
I had a similar experience with my now 17 year old cat. When he was much younger and more adverturous he became very lethargic, not eating, trying to heave something up, but couldn't. After a couple of days I began to see irregular pieces of a brightly colored substance in the litter box. Turned out to be balloon fragments from my daughter's birthday party. Once he got it out of his system, he was fine. Tape, I don't know. Seems that could be more problematic.
Too bad about the Skylarking tape. I hope it was replaced with a less tasty CD.