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.