SharePoint Designer: throwing error while open my sharepoint web applicaiton

Question

When i try to open web application in sharepoint designer. I can't able to open it throw error like this
An Error occured accessing your Microsoft sharepoint foundation site files. Authors - if authoring against a web server, please contact the webmaster for this server's web site. WebMaster - please see the server's application event log for more details

Answer 1

This error occurs if you try to use a reverse proxy to rewrite the response body contents for a SharePoint site as well. We were attempting to inject a Google analytics tracking javascript in the body of all responses. The code never did show up
successfully and this error message resulted as well. We eventually discovered a web solution out on Codeplex that allows you to add the Google analytics tracking script. This article hinted at the root cause:
http://support.microsoft.com/kb/329362/en-us