Today updates to all extant macOS editions of Mountain Utilities applications were released:

• A-880 Manager 3.1.0.1
• BC Manager 4.0.2.1
• FCB1010 Manager 2.1.0.1
• MIDI Tools 2.1.0.1

All these updates can be downloaded from their respective download pages.

These updates should make the update checkers of these application work correctly again, at least on OS X 10.9 (Mavericks) and later.
See comment #8 in https://mountainutilities.eu/forums/i-get-error-opening-fcb1010-manager for full discussion.