Ran into an issue today with trying to import an Excel 2003 spreadsheet into a SharePoint list. SharePoint would load Excel, then you select the cells in Excel that you want to import, you click Import and Excel responds with "Cannot connect to the server at this time." After a long while searching for a solution, I came across the following link:
Basically the solution was 2 workarounds:
a.) Import the spreadsheet into a root site, then create a list template and use that to create the list within a subsite.
b.) Use Excel's List Publishing feature to publish directly to the subsite.
I tested both options and they each worked equally well, I ultimately went with option B as it seemed a cleaner solution.