Can't go through Proxy

Hi all, Am trying connecting to our MS Proxy (ISA) using my SuSE 8.1 Pro for browsing the Internet, I can't and receiving this message: Unknown Authorization Method Anyone know how can I solve this Big problem? Thank you, Mohammad R. Al-Harbi System Administrator APICORP TEL: 966 3 8597338 FAX: 966 3 8470011 GSM: 966 55 827212