W. Watson wrote:
Solved the problem. I put liquid wrench on the nut, grabbed the saw with
a rag, put a wrench on the nut and twisted. Still couldn't get it off,
so I took it to the hardware store, and asked the guy who sold it to me.
He did the same thing but got out a hammer and whacked the wrench a few
times. Off it came. I've now oiled the arbor threads.


I will quote from my previous response:

If you put on some good leather gloves and hold the hole saw, put a
wrench on the nut and tap it with a hammer, it usually comes loose.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX