When connecting an Ethernet interface (R1-Fa0/1) to another Ethernet interface(R2-Fa0/1) that is part of a bridge(R2-BVI1), you can ping from one side (R1-Fa0/1) to the other (R2-BVI1). When connecting a Frame Relay interface(R1-S1/0) to another Frame Relay interface(R2-S1/0) that is part of a bridge(R2-BVI1), you will encounter a problem with encapsulation. On one side (R1-S1/0) sends packets with Frame Relay encapsulation, and on the other side (R2-BVI1), packets with an Ethernet-ARPA encapsulation are expected. The only solution here is to create one bridged interface on each side (R1-BVI1, R2-BVI1).