Inflow at Outflow error message

Ben

Hello all.

I have built a simple rotating mesh. It is a cylindrical pipe, rotating about an axis parallell to its axis and offset by about 7 millimeters. The pipe is 30 mm long and 5 mm in dia.

I keep getting this error message that says something about inflow detected as some outflow boundaries where mass fluxes have been forced to zero. I think I understand what it means, but I don't know what might be causing this. I have been through the model several times. Can anyone help?

Thanks