I have the same problem. I created my site on Saturday, so it's only been around for 3 days. Yesterday afternoon, my option to edit with Sitebuilder was gone. I noticed by website is also now flagged as a "custom website". I tried some old bookmarks, and got in to Sitebuilder again, but now whenever I try to publish I get an error that 1 directory or another "cannot be created". Something happened (maybe something I clicked that I wasn't supposed to) and now my site no longer thinks it's a sitebuilder site. Also, it's interesting that I cannot create a new site either. If I click to create a new site, I get a "this page cannot be displayed" message.