The request failed with HTTP status 407: authenticationrequired

Hello.

I developed an application that invoked a web service, from IDE Visual Studio 2008 runing on Windows XP, it works fine, I could debug.

Then change the PC to Windows 8, with the same Visual Studio (2008).

The same app web crashed. I got the following error: 

Message: {"The request failed with HTTP status 407: authenticationrequired."}

Response.Headers: {Proxy-Connection: Keep-Alive
Content-Length: 4445
Cache-Control: no-cache
Content-Type: text/html
Proxy-Authenticate: NTLM,Basic realm="McAfee Web Gateway"
}

StatusCode: System.Net.HttpStatusCode.ProxyAuthenticationRequired

Regards