I have the same problem accessing my work exchange webmail. I can also access it from everywhere but on my network. When i try and access it, I will get my login and the template for the page, but once I try and login it will continually bring up my login again, and again. I can ping the dns no problem and get the same error when trying to access it by IP. I am not sure if it is something on my side(firewall) that is blocking this site. If you have any help, please reply back.