ISA Server blocking shockwave

It looks like our ISA Server is blocking shockwave from being installed.

Using the following link http://sdc.shockwave.com/shockwave/download/triggerpages_mmcom/default.html we get to the download page and the Shockwave Install window appears but then we get “network error” please try later.

If I then elect to bypass the ISA server, I can download and install shockwave with no problems at all. Can anyone point me in the right direction as there is nothing in the log files.