Running Diablo II in -txt mode? Not anymore!

I'm not sure which forum this is more relevant to... Sorry.

I've stepped away from Diablo II for a while and I came back to one of my mods last week. I run it with the -txt command appended, which makes the game read from data files stored in the install directory rather than the game's supplied data archive. Now it doesn't want to know. I haven't repatched it or altered any of the game's core files in months; I reinstalled it from scratch, ripping everything out, no dice. The same problem has occurred on a different install of the same game with a different patch version on a different machine. This eliminates any chance of the game itself being the problem (I hope).

I'm using Kerio's firewall and that is the only common factor between these two machines. Unless there's been a Windows update (not using SP2 yet) that I did not notice that suddenly prevents you running third party software with appended command lines, I'm stumped.

Any ideas?