Pump flow reverses

Hi Everyone,

I'm a new user and got this WaterGEMS error "Unexpected Reverse flows calculated" at one of the pumps. In the capture below, the highlighted pump are the one causes this error with its pump pattern attached. I think the pump in Watergems is automatically installed with a check valve which protect from reverse flow, so I wonder why still I got this reverse flow on the pump link and any idea where I may check to make this work?

Thanks for the help.