Can you please ping the broker you are trying to access and see if it responding? It could be a network problem.
I tested the secure_mqtt snip which connects to test.mosquitto.org server and it works fine:
IPv4 network ready IP: 10.40.2.133
Setting IPv6 link-local address
IPv6 network ready IP: FE80:0000:0000:0000:A608:EAFF:FED9:C0CE
Resolving IP address of MQTT broker...
Resolved Broker IP: 126.96.36.199
[MQTT] Opening connection...OK.
[MQTT] Waiting some time for ping exchange...
[MQTT] Received HELLO WICED for TOPIC : MQTT/WICED/TOPIC