Why is my simulation not working (boundary face error) though geometry check appears to be clean?

Hi,

I'm pretty new to flowsim and currently having many problems regarding all kinds of errors. Geometry check is fine in the model below, though there is some threads interference (screws and nuts). The face of boundary error is blue highlighted in the image (inlet flow). What can possibly go wrong and how can I address it?

SolidworksFlow Simulation