I am designing a microfluidic chip with a number of inlets and outlets that all connect to a common chamber. One particular inlet and the outlet have serpentine channels linking them to the common chamber. When I try define boundary conditions (inlet volume flow/environmental pressure) on those particular ports I get the "unresolved boundary condition" warning when I run the simulation. I do not have this type of trouble when the boundary conditions are set on the other inlets and I use one of the inlets as the outlet,and the simulation works fine. The designs of the inlet/outlet are all exactly the same. Is there a particular reason why some inlets work and some don't? Does it have to do with the serpentine channels? Any help is appreciated, thanks.