I am having a problem isolating this problem, and how to correct it. The problem is described elsewhere:

http://www.gamesas.com/texture-load-error-imperial-broadsword-blade01-t271701.html

But unlike this users results, I still have the same problem after taking the same steps. When I enter Fort Moonmoth, I get two errors pop up, both evidently caused by the same problem (see above link). Closing the error windows, I am able to proceed into the castle. Subsequently, I am able to go in and out of the castle again, but with no more errors displayed. When I save the game and then reload that game, I get the same errors again. When I buy the sword listed in the error message, and attempt to equip it, the game crashes to desktop. The solution seemed to be to reinstall the Darknut's replacer, which I did, but to no effect.

Are there any good suggestions as to what I can do to troubleshoot and correct this?

I had that problem once as well. like in the thread you've linked to, re-installing the mod solved the issue for me.

maybe the problem has to do with your merged_objects.esp (just reupdate it).

Done... no joy.

Edit: I take that back. I did a Mash lists update. How do you do a merged objects?

Check if you have TX_W_Imperial.Broadsword_blade01.bmp or TX_W_Imperial.Broadsword_blade01.dds in your textures folder.

Btw. I checked my folder and I actually have tx_w_imperial_broadsword_blade01.dds in my textures folder (i.e. with underscore instead of the dot there). Do you have NifScope installed? If so, open Mashes\w\W_Broadsword.Imperial.nif and check which texture is written in the model file just to be certain.