Netconf on Cisco 3750

WS-C3750-24TS running c3750-ipservicesk9-mz.122-55.SE8.bin

DLS1#sh run | i netconf
netconf max-sessions 16
netconf ssh

You must have the correct header in order to communicate via netconf.
On a 3750 switch the correct header is:

<?xml version="1.0" encoding="UTF-8"?>
<rpc message-id="101" xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:cpi="http://www.cisco.com/cpi_10/schema">
</rpc>]]>]]>