access denied by access control list

Hi, i have a problem, i’m trying to give access to a PC to the internet throught the company’s proxy on port 8080. the problem is when i open explorer and try to browse i get the error message “page is not available acess denied by access control list”. also all other application that use internet are not working.

network connectivity is working properly.
telnet to the proxy on port 8080 is successful.
OS: windows 2000 advanced server
browser: internet explorer 6.0