A.The switches are not the same model.
B.You are not using the correct SFP.
C.You are not using correct optical media converters.
D.Configuration should be modified， because the distance is longer.

A.Because Frame Relay IETF encapsulation is only configurable at interface level， you must use IETF encapsulation on all routers.
B.This is not a possible scenario. A dedicated Frame Relay link to RemoteB is mandatory at the central office.
C.The router at RemoteB must be replaced by a Cisco router.
D.Use Frame Relay IETF encapsulation on a per-VC basis on the central office router.
E.There is a problem in the Frame Relay cloud， because Cisco routers are compatible with IETF Frame Relay.