I found it.
R3 and R4 were not already OSPF Neighbors. They are connected through Frame relay. R3 interface is "point-to-point" OSPF network type. R4 however, has interface ser0/0 in "NBMA" OSPF Network type.
I corrected the network type under ser0/0 of R4 and it works
Forum Tips: 1. Paste images inline - don't attach. 2. If you find my post helpful, please give it a thumbs up or mark it as a correct solution; You never know in the future who you might help doing so..