Unfortunatelly your suggestions didn't work:
MOV DX,OFFSET USAGE_LINE and LEA DX,OFFSET USAGE_LINE.
I tried to put an ORG 100h in the DATA_SEG part too,
that did not work either. Disassembled the line would say
MOV DX,0100 though, but the string started at offset 0210h!
I think I'll use a...