Do you have veriloga in the stop list of the netlister (Setup->Environment)? If so, it shouldn't be, since there is hierarchy within the veriloga view. Note, the same thing applies if you're using a config - veriloga should not be in the stop list in the config.

Is the subckt for B appearing in the netlist?

Try modifying the veriloga view for M (add a blank line) and save and exit the editor - this will re-trigger it to be parsed, and it should then update the cellView with information about the hierarchy. Provided you're using IC5141 or earlier, you might want to look in library directory structure, under the cellView M/veriloga, and look at the file pc.db. This file should indicate any cellViews instantiated within M - and this is how the hierarchy expansion at netlisting time knows to netlist B. The pc.db file is ASCII, so can be inspected easily (don't edit it though...)

Regards,

Andrew.