Error “%VRF specified does not match existing router” suggest that you have already configured an OSPF process for particular VRF.
R2(config-router)#router ospf 1 vrf cust1
%VRF specified does not match existing router
R2(config-router)#router ospf 1 vrf cust1
%VRF specified does not match existing router
R# do sh run | sec ospf
router ospf 100 vrf cust1 –<<<
redistribute bgp 1 subnets
network 12.12.12.2 0.0.0.0 area 0