I have seen a picture of the letter. It does indeed say "therefore not suitable for a LTC..." and "You have xxx days to surrender your firearms, ammunition, etc.".
This wasn't an administrative hold or a "hey buddy, that check bounced. We can't proceed without the fee." letter. This was a denial of a renewal.
As to the "how could he bounce a $100 check?" question. I don't know. It was drawn on a joint account right about the time that they started parting ways. Lot's of shoulda-done around this.
I guess the real question is how to proceed?
Call and offer to pay the missing money? - Since this made it to a full on surrender your stuff denial, I think that time is past.
Appeal the denial? - Maybe. Get before the judge, say I'm sorry and I have a postal money order for $100 in my pocket... can I have my license please?
Submit a new application? - Pay with money order this time and check the "yes, I have been denied" box with a "I bounced the renewal fee check" explanation?
I suspect that one of these results in a few more months of waiting, but a LTC at the end. One probably results in years of waiting and a lawyer. Not sure which one is which.