Problem: While importing the Excel spreadsheet in Sharepoint, you get the error message " "Method 'Post' of object 'IOWSPostData' failed error."

Solution: The solution that worked me was the one give below,

Open your browser and go to the "Tools" menu - Internet Options - select the "Security" tab - Select the "Local Intranet" icon, click the "Sites" button, then click the "Advanced" button and add your domain (e.g http://sharepointsite/) in the local intranet zone.

If this doesn't work you can aslo try following this solution