UBCD50b12 has fdubcd.igz instead of dosubcd.igz.
UBCD hasd dosubcd.igz (so you should rename fdubcd.igz to dosubcd.igz), but I am not sure if the last fdubcd.igz works with UBCD411 (some earlier revisions did work). Donwload UBCD50b12 if you want to have a working version.
OK -- I downloaded fdubcd.igz, renamed it to dosubcd.igz, and replaced the existing dosubcd.igz -- no joy!!
I also downloaded UBCD50b12 and burned the iso to CD via burnatonce. No joy here either!!
I always get the "memory management" screen with the options 0-6. Why? (Is this WAD??)
I have tried various options (0 through 6) -- but most of the tools do not run properly. When option 0 is selected, I get the PANIC, MCB chain corrupted. Other selections dump me to drive Q: and fail to start the app just, or issue some other error.