This mission was made back when version 1.4 was all we had. sent Hazelwood, E mail, but no responce yet. So assuming download from his site is good, & you are running version 1.4 stock, if Single Mission opens in mission editor, & you have no Mods changing scriped units, it should work.
Now I know that is a lot of IF's, but worth a try. Gun boat,& shore batt./shallow water, make this one tough mission/cookie LOL. Run decks awash @ flank, & evade thru Bay/Harbor. "I'm going down," does deck gun work on Gun Boat.
I think getting the right folder installed in the game, is the trick to it's running proper. Brake it down for look see ?