There are few steps you will have to take before WebADI can be properly used:
Follow the steps below given in the screenshots and apply the settings exactly as they are depicted. The screenshots are from Excel 2010, however the settings should also work for 2000, 2003, 2007 versions.
B) Open Microsoft Excel –> File –> Options –> Trust Center –> Trust Center Settings
Now log out from your Oracle Applications and re-log back in. Retry the Web-ADI upload.