How to connect two part divided by interface
 

hi, everyone!
there are two parts in my gambit mesh. they are connected by two faces. I defined them as interface, interface_A and interface_B. I followed
the instruction in web
http://openfoamwiki.net/index.php/Howto_importing _fluent_mesh_with_internal_walls

but when I worked on splitMesh
In my case forder
splitMesh interface_A A1 A2
there are err message

Read 176 faces to split

Face 439300 in faceSet interface_A is not an internal face.

From function splitMesh
in file splitMesh.C at line 146.

FOAM exiting

anyone can tell me what wrong with it.
How could I connect the two parts after fluentMeshToFoam.
Thanks!