502 Proxy Error. The request is not supported. (50)

Technical Information (for support personnel)
Error Code: 502 Proxy Error. The request is not supported. (50)
IP Address: xx.xx.xxx.xx
Date: 5/13/2007 3:34:54 AM
Server: server name
Source: proxy

answer for this problem is:
ISA Server mmc console – Configuration > Add-Ins > tab Wel Filters > properties Compression
Filter > select Enable This filer. > Ok > Apply.