Sat Mar 21, 2015 1:31 am
Make sure that both neighbors agree on all of the parameters - IP network / mask, network type (broadcast, point-to-point, multipoint, etc), and even MTU. (IP MTU)
Make sure both neighbors actually consider the interface as a part of OSPF, and that they agree on the area ID, and area type.
Make sure that you have a backbone area and that it is contiguous (in fact, I recommend all routers use 'backbone' area while you're new to OSPF and don't have a huge network with tens of thousands of routes)
If you have authentication enabled, make sure you have that configured the same on both sides.