Request you to Go to Settings->App Settings and Edit the values as follows:

MAX SIMULTANEOUS READ / WRITE REQUESTS PER IP: 2

MAX SIMULTANEOUS REQUESTS FROM THIS SERVER (in which iwp is installed): 3

TIME DELAY BETWEEN REQUESTS TO WEBSITES ON THE SAME IP (milli-seconds): 200


If the above settings do not work as well, try setting them as follows: 

MAX SIMULTANEOUS READ / WRITE REQUESTS PER IP: 1

MAX SIMULTANEOUS REQUESTS FROM THIS SERVER (in which iwp is installed): 1

TIME DELAY BETWEEN REQUESTS TO WEBSITES ON THE SAME IP (milli-seconds): 200


If the first set of settings work then try increasing them slowly to a number that works for you.