We are integrating with Salesforce and using SOAP API for the same. We are able to log in and log off successfully and after 3-4 attemts it gived below error on login. Attempts are not fixed. Error  can come after any no of attempt
"An unexpected error has occurred: The remote name could not be resolved: 'login.salesforce.com'   at System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)
   at System.Net.HttpWebRequest.GetRequestStream""
When the above error comes then we also tried to browse through IE on same machine and page can't be displayed error comes. And after 3-4 Min everything again starts working well.
Any help would be highly appreciated. Its urgent.

I am increasingly receiving this error when accessing web services: DNS is OK.

 The service will be unavailable for hours at a time then start working again.

Has anyone come across this?