Windows will only make outbound TCP/IP connections using ports 1024-5000 by default, and takes up to 4 minutes to recycle them. So in the case of runnung a load type performance tests the port range is filled pretty fast.
To allow higher values for ports on Windows add this parameter to the system registers:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
subkey in the registry.
MaxUserPort
.
65534
as decimal.