Tractor wouldn't start. Changed magneto and it started. I shut it off and it wouldn't start again. Checked plug for spark and none. All wires and connections appear good. Any suggestions would be greatly appreciated.

Did you gap the magneto at 010.

Yes I did. Rechecked also.

Remove blower housing , unplug ground wire going to magneto,
If you have fire then ,it could be wire going to ground some where , or bad saftety switch some where.
Luck

Unplugged magneto ground and still no spark. Is it possible that I have a another bad magneto?? Or should I be looking somewhere else?
Thanks

Yes the old business card gapper.

Very possible.
That's the way I gap them also.

Is it possible that I purchased a bad unit?
Or is there something else I should be looking at?

If you have it unpluged at the magneto and no spark its bad.
Luck

OK. Here's the deal. I put in new (2nd)coil... it started. I ran it for a min. shut it down. Started it again 5 minutes later and figured I could put it back together. 1 hour later... back to square one. No start. Any idea what could be going on here?? Never seen this before.

Well took it the shop... was told that coil was bad. Replaced it a third time. Told that it started about a dozen times over the past day. Got it home... and what happened?? Not a thing. Just cranking and no start.