The daemon had trouble parsing the json you sent it.
Without a code snippet, I can't help you any more than that.
/* Configuration variables for the JSON-RPC server */
$rpc_host = 'localhost';
$rpc_port = '8332';
$rpc_user = 'thisuser';
$rpc_pass = 'mypass';
require_once('jsonRPCClient.php');
$bc = new jsonRPCClient('http://' . $rpc_user . ':' . $rpc_pass . '@' . $rpc_host . ':' . $rpc_port);
Also conf:
# JSON-RPC options (for controlling a running Bitcoin/bitcoind process)
# server=1 tells Bitcoin-QT to accept JSON-RPC commands.
server=1
# You must set rpcuser and rpcpassword to secure the JSON-RPC api
rpcuser=thisuser
rpcpassword=thispass
# How many seconds bitcoin will wait for a complete RPC HTTP request.
# after the HTTP connection is established.
rpctimeout=30
# By default, only RPC connections from localhost are allowed. Specify
# as many rpcallowip= settings as you like to allow connections from
# other hosts (and you may use * as a wildcard character):
#rpcallowip=10.1.1.34
rpcallowip=127.0.0.1
rpcallowip=10.1.10.100
rpcallowip=localhost
# Listen for RPC connections on this TCP port:
rpcport=8332