Thanks for the fast response. Yes, the problem is related to the type IXc.
About the RR files being 0kb; you say they are not needed for your mod, but they
are included. So if you install your mod they will replace the original RR files.
I'll go check if the problem goes away if I have your mod installed, but have the
original NSS_Uboat9_RR.* files in place. That way, you won't have to fix anything either; you can just remove the 0kb NSS_Uboat9_RR.* files from your mod.
(But let me know if I'm saying something incredibly stupid here
)
Anyway, I'll get back to you after testing.