This is happening in between PE router and CE router. Immediately after configured the neighbor command on CE router, connectivity to CE router lost. Telnet management of CE router has been enabled through PE router, so whenever WAN connectivity lost management(telnet) too lost.
When check BGP neighbor table from PE router at that time, BGP neighborship was formed. Also other side(CE router) too shown neighborship is ok(this is checked by tech team by console login @ CE router side) but ping to WAN IPs not work(ping time outs). No any error message received to the router until debug the CE router for BGP. then getting attached error message.
PE router details are: Cisco IOS XR Software, Version 5.1.3.>>asr9k-os-mbi-5.1.3.sp3-1.0.0/0x100000/mbiasr9k-rp.vm
CE router details are: "flash:c800-universalk9-mz.SPA.154-3.M3.bin"
I was trying so many things to fix this. It was noticed immidiately after remove the neighbor command from CE router again WAN connectivity is ok(ping & telnet management ok). When check BGP neighbor table it was found more than 300 prefixes on BGP table. Finally I found a way to temporally fix it by limiting BGP prefixes to very limited value(first it was 5) by using a "ip prefix-list" under the BGP process. But this is not acceptable by my customer because he need to have full routing table(all the BGP prefixes) in CE router. Please answer my question if any one had come a cross this issue previously.