What is that? I'm on it! ...
Apparently that GBS is setting to a non-existent bank (four banks, trying to select the 26th one). My current code uses bank 0 in this case, and I think that may have been necessary for some other GBS files. If the number of banks is a power of two, the hardware-wise thing to do would be to use the modulus (second bank in this case). The change is simple:
// Gbs_Emu.cpp line 74:
if ( n >= bank_count )
dprintf( "set_bank out of range: %d, bank_count: %d\n", (int) n, (int) bank_count );
n %= bank_count;
I should test the new GBS music that's been released. I'm just so put off by the umpteen-page threads of people haphazardly posting new rips and links to pages of random collections. I wish they'd get together and makte a centralized site that accepts submissions using an automatic script.