In LLD rule I call zabbix agent
system.run[/usr/local/zabbix/agent/scripts/list-files.ldd '/opt/crl/ready/']

which returns JSON:

{
    "data":[
        {
            "{#FILENAME}":"crlinfo.txt"
        },
        {
            "{#FILENAME}":"fk01.crl"
        },
        {
            "{#FILENAME}":"new-last.crl"
        },
        {
            "{#FILENAME}":"test001.crl"
        }
    ]
}

It is fully valid JSON, but zabbix has an error: 'Value should be a JSON object.'

This JSON is generated by python:

print json.dumps(outjson, separators=(',', ':'), indent=4)
print

why do you use your notation of JSON and don't follow the standart?