Not able to update Specific vpn interface

Steps:
=====
->Configure 2 vpn instances testVpn1 and testVpn2
->Create vpn interface s1-eth1 for vpn instance testVpn1
->Update vpn interface s1-eth1 for vpn instance testVpn2

Error observed from REST conf:
=============================
http://localhost:8181/restconf/config/l3vpn:vpn-interfaces/vpn-interface/s1-eth1/
Response Body
{
"errors": {
"error": [

{ "error-type": "protocol", "error-tag": "invalid-value", "error-message": "s1-eth1 from URI can't be resolved. " }

]
}
}
Response Code
400
Response Headers
{
"Access-Control-Allow-Origin": "http://localhost:8181",
"Access-Control-Expose-Headers": "",
"Access-Control-Allow-Credentials": "true",
"Server": "Jetty(8.1.15.v20140411)",
"Transfer-Encoding": "chunked",
"Content-Type": "application/json"
}

No error logs observed in karaf.log
Configurations are attached.