Anglo, you may think me daft, but I never figured out how to display a score in Barfly. But when I actually bothered to read the documentation, I discovered split-screen mode, and encountered the same error.

The cause of the problem is simple: delete the "V:1" line right after the "K:A" line. I had earlier used simple numbers (1, 2, 3) for voice identifiers, then switched to prefixed ids (V1, P1, P2). That line was a holdover I neglected to remove.