Load test in SoapUI shows error "NoHttpResponseExcption: Target server not responding"

Hi,

While running a load test i have observed one strange issue, whenever the count of total message request crosses 100, I can see the error "NoHttpResponseExcption: Target server not responding"

This is strange because it is even failing with lesser number of threads(20) which run for long duration or more threads(50 or above) running for short duration. In both the cases when "Cnt" reaches 100 we see the above mentioned error. We have looked into the Upstream /Loadbalancer server settings but nothing worked out. My client is asking me to check the SOAPUI settings. Can you please assist me and let me know if any other details are needed.

SoapUI: 5.4.0

Web Services: Rest Services with AMQP

Thanks