I had a wierd problem that had an even wierder solution. For a certain site I had to give my users an IP URL, ie http://188.8.131.52/read/ as a temporary work around for a browser config problem. I run a network that spans 2 countries, I have a site in Noumea and one in Fiji, Fiji is linked to Noumea via satellite, I have a web proxy in Fiji that connects to the proxy in Noumea from where it connects to the Internet. From Noumea the URL works fine, from Fiji they got this.
The page cannot be displayed ..... ......... Open the 184.108.40.206 home page, ...... ..... 64 - Host not available Internet Security and Acceleration Server
so I start to take a look at the Suva ISA box and find a routing rule that the admin over there had stuck in, it was totally useless as what she was trying to do is set in the browser anyway, she had created a rule to bypass the proxy for *.spc.int, that being our local domain. This is set in all browsers anyway, ie don't use the proxy for *.spc.int. I didn't see how this rule could affect someone trying to browse a site by IP address but I disabled it anyway, when I did that the IP URL worked ?
The only explanation that makes any sense is that the ISA web proxy does a reverse lookup on the IP number URL, sees that this resolves to lyris.spc.int and enforces the rule to not use the proxy for *.spc.int and of course cannot connect to the server because it is outside our local network (and hence why I was using the IP number URL in the first place), having "don't use proxy for *.spc.int" set in the web browser works correctly ? and uses the proxy for the IP number URL.
Can someone confirm this is by desgin ? because it is inconsistent with how IE and most anything else works.
I also had the same problem but the problem was solve. This is a DNS issue. The DNS cannot resolve/delayed responce the site that you wan't to browse and ISA Server returns this error message. This is usually an ISP problem if you have one.
Work around : You should install DNS(Cache Mode) on your internal network to resolve this issue.