What would possible causes be?

To explain: I have a set of 3 sound sources: the basic sound generating unit (SonicCell) plus 2 expansion cards. I tripple checked my calculations for bank numbers - MSBx128+LSB
All banks are loaded fine by Producer, except 4.
Why this is a mystery to me, is that on the basic unit the 3d bank and 7th bank are not read, while the 1st bank of each Expansion slot is not read. Again, I have checked each patch number 3x
Any ideas, please?
Thanks