I had that error message when refilling tub which was caused by an airlock. I removed the filter, placed my submersible pump in the tub and put the outlet hose into the hole where the filter screws in. Cleared it on about one second. 😊 I had heard you might be able to use a hose with a strong enough flow or try to plung water through the filter hole by turning the filter upside down and plunging. I tried those but only was successful with my submersible.
