UDP problems

I am using RCM3710 and having problems with networking. I have a design that has been working well on its own network but now I need to run it on a general network with other data. I originally set the Remote IP to but if the PC I need the module to talk to does not get a message in before others the module never replies to its queries. Tried changing the Remote IP to which is the ip of my PC but after receiving the packet it has an error when trying to send. the return value of udp_send is < 0. retval = udp_send(&sock, buf, length);

Tried 0 but this is the same as Tried -1 but I get an error when trying to send as when using

Here is my call.
if(!udp_open(&sock, local_port, resolve(REMOTE_IP), remote_port, NULL))
local_port=2003, REMOTE_IP is 0 or or and remote_port is 2003.

What could be the problem