I've attempted to upgrade from 5.4 to the new 5.5 on a test site (before a full install on my primary site) - test.dontworrypeehappy.com -- this worked fine - I even upgraded to the newer version of my ecommerce plugin to test that as well - no problems.

Now, I go back to my main site (dontworrypeehappy.com) and click the link for updating to 5.5 - I get a "page not found" error --- and for some reason, my ecommerce plugin has gone missing from my primary site.

Any suggestions?