I created a user parameter on zabbix agent, that is calling a script. Got the following output from zabbix_get:

ZBX_NOTSUPPORTED: Invalid result. Non-empty output is expected.

After spending some time, trying to understand why my script produces empty output, finally found in agent log:

  4135:20140801:115742.739 zbx_popen(): executing script
sh: 1: /home/phil/ldd.sh: not found

I believe, in such cases agent should report this to server, e.g.
ZBX_NOTSUPPORTED: Executing script: /home/phil/ldd.sh: not found