Cannot link my site to SP 2010, says it is not a SP site

Hi,

I am trying to link my site to SharePoint Designer 2010 however, I receive two error messages when entering the URL:

The first says "default.aspx is not a valid folder name."

The second says "Microsoft SharePoint Designer does not support editing non-SharePoint sites."

My site is hosted by SharePoint and I am curious to know how I can resolve this issue and connect my site to SPD.

Thank you!