Here’s a quick one:
If you want to import excel file to SharePoint (create->import spreadsheet), you have to have a site collection provisioned in the root managed path in order to connect via excel. If not, you will get “Method ‘Activate’ of object ‘_Worksheet’ failed” error.
In example, if you are working in the site : http://server/sites/itaysk, you must have a site in http://server/ for the import to work.
-- My name is Itay Shakury and I’m a SharePoint consultant --