I am using a 3-d grid created in gambit. I have 1 interface boundary. When I want to initialize the problem, it results in the following error:

WARNING: Unassigned interface zone detected for interface 4 Error: Init_Flow: unassigned interface_zones Error Object: ()

What's the problem?

To define an interface you will require two interface boundary conditions (one on either side of the interface). When mesh is imported to FLUENT the interface must be defined using the define->grid interfaces menu. This tells FLUENT which interfaces to interpolate the data between.