You are getting the hang of this rather quickly! Excellent find. Now, take the Data / Roster / British / Sea / DDClemson.cfg and rename it DDTown.cfg - looks to be the simplest "fix" for it... If you open the Clemson file in the British folder, you'll see that it's referring to "ClassName=DDTown"
Edit: Another thing you can do to "test" a game is to run the Museum. Make sure you have LAA enabled on the SH4.exe file first though... If it crashes, that usually means there are issues with the ship just after the crash. Some mods just will not run the Museum, but it's not always the ship definitions. I'm trying OpMonsun's now...
Edit2: 1st run crash after B17G in the US planes (... Ships "fly" across the screen too...
... well, the "US LB HeavyBomber" and the "AM B24 Level Bomber" both crash it... This might take a while... lol
Edit3: OK, there are file name mis-matches, as well as ClassName mis-matches, so while I wait on other happenings, I'll noodle in OM for a bit, and go through things and try to match them up, and get back with you...