Yamaha SY55 Product Manual page 148

Miscellaneous Error Messages
1 4 6
Internal battery voltage low. Have battery replaced by qualified YAMAHA
service personnel.
Internal voltage malfunction. Have the unit checked by qualified YAMAHA
service personnel.
Voice With mismatched wave card ID exists in multi-play setup.
Wave card not inserted in WAVE slot.
Voice ID and wave card ID do not match.
Voice number and voice type do not match.
Wrong bulk dump byte count or unrecognizeable bulk, memory or card
data.