[Serusers] Problem with SER/SEMS

Hi I am trying to setup SER/SEMS using unix_socket. I am trying out the echo app using if (uri=="sip:200@xxx.xxx.xxx.xxx") { t_relay(); if(!t_write_unix("/tmp/am_sock","echo")) { t_reply("500","error contacting sems"); }; break; }; however the phone connects and the call timer start to run but no echo and the following in syslog May 1 14:22:46 localhost ser[18236]: ERROR: _reply_light: can't generate 500 reply when a final 513 was sent out May 1 14:22:46 localhost ser[18236]: unixsock_t_reply: reply failed May 1 14:22:46 localhost ser[18236]: unix_server_loop: Command 't_reply' failed with return value -1 May 1 14:22:46 localhost Sems[18061]: Error: (AmRequest.cpp)(reply)(335): AmRequestUAS::reply: 500 Reply failed Any ideas what is happening? -- Jon Farmer Telford, Shropshire, UK