SWTPC 4K BASIC and 8K BASIC 2.0 expect the MP-C board for the console
interface and are incompatible with the MP-S board. 8K BASIC 2.2 and
later are compatible with the MP-S board.

A patch to 8K BASIC 2.0 to work with the MP-C board is in the file 8K20PAT,
but you might as well just run version 2.2 of 8K BASIC instead (SWTBAS22.S19).