So what are you using for the source IP address now? You should always specify the source on an iBGP session; I think it will simply use the IP address of the outgoing interface otherwise, and depending upon topology, link failure etc., this may change.
As this is an iBGP session the peers do not need to be directly connected, but is there an IGP route that allows connectivity between the source and destination IP address?
A little more detail of the topology between the ERL and the other BGP router is needed.