Error Code: 502 Proxy Error

Hello all, i am using ISA Server 2004 Enterprise Edition with Sp3. I am experience some problem with my ISA server. whenever i want to click visit some sites i am receiving such type of error from ISA Server .

Error Code: 502 Proxy Error. A software error occurred for a Windows Internet extension application that is required for the current operation.
How i can solve this Problem.
Secondly how i can allow Live Update oF NOD32 Definition on ISA Server.

Thanks
Muhammad Usman