Separator error may be caused by:

Extensive foam build-up in the liquid separator.

Check the separator assembly and connections for possible air leaks.

Waste-tube between liquid separator and waste pump is blocked.

Replace the tube.

Waste-tube between waste pump and waste container blocked.

Replace the tube.

Waste pump failure.

Exchange the waste pump cassette. If the error returns, call for service.

Electrical bridge between the waste-level electrodes.

Clean liquid separator, see Cleaning liquid separator