Repeating classes wouldn't result in a crash.

Looks like it really is back to square one then.

check the entire side. Ie req's/odf's (specifically weapons and all_inf_default_rifleman(the default odf). Check commas and " symbol (quotations) I would also call the repeated unit class something else, and completely look through the LUA yourself (we have done that a lot for you know so if you think its good its good) Completely manual clean, munge, and try again. Post the results and the error log. Beyond that try removing one unit at a time until it works. replace the unit that was crashing it to prove that unit crashed the map, then fix it. Also, look through your world folder make sure everything is there (sky file I think, dunno.) and the ODF's and .mshs are okay. AFTER you did the above, re-start. Its crashing for no reason and something is corrupted. Sorry to tell ya that man, I know it sucks

I looked through the side file and there are no flaws in the odfs or the reqs. What a frustrating experience this is turning out to be.

That era tutorial is here: forums/viewtopic.php?f=27&t=27616

One thing you should do is remove all other mod maps. Since people keep forgetting to update AddNewGamemodes() to use MergeTables(), it's possible another mod map is wiping out your additions (or you're wiping out there's).

You do need to make sure your map works before you change eras (or any other major change/addition). Only try one new thing at a time and keep backups of when it was last working.

I don't remember that Lua error, I don't think you should be getting it. Guessing, I'd say it's an addon.lua issue. Can't say if it's from your map or a different one.