Is it possible to add a new faction?

[Aenlic]

The error looks like it's in the unit_prod file. When loading the unit file, it came to an entry for an STW_Ashixbow that it doesn't recognize. Unit names are initialized in the /loc/eng folder in the names.txt about 2/3 down in the file. You'll see the unit names down there and also the singular/plural names. If you've added a new unit name to the crusaders_units_prod11.txt or whatever file you're using for your units, then you also need to add it to the names.txt in the appropriate places. If it wasn't a unit that you added, then it seems like that might be from a mod. Did you recently install the STW mod?

[Shaka_Khan]

Thanks for replying.
Yes, I installed the STW mod. Will initializing new units allow me to play them against or under MTW factions?

[Aenlic]

There should be some guides in the Repository forum here. It's the forum listed right above the Alchemist Lab where we are now. The guides explain how to add new factions and units. Here's a good place to start, from that forum https://forums.totalwar.org/vb/showthread.php?t=31892 with good information on adding new units, or like I think you're doing, adding an STW mod unit to the other MTW campaigns.

If you're not doing that, then I'm unsure how to help.