Problem in upgrading Microsoft Sharepoint

I want to upgrade my Sharepoint office 2007 to Sharepoint designer 2010. It is to mention that I use a shared server with installed front page extensions.
Though I built it using Sharepoint office 2007, but when editing with Sharepoint designer 2010, it shows an error message which is shown here:

Why is this fallacy? Should I use a Windows server to solve the problem?
If, yes, then what should be the provider?
Any help will be gracefully accepted.
Error:
Microsoft SharePoint Designer does not support editing non-SharePoint sites.
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