I was running the Selenium C# script and had my test data in excel and when the script was running I was getting the following error.
System.InvalidCastException : Unable to cast COM object of type ‘Microsoft.Office.Interop.Excel.ApplicationClass’ to interface type ‘Microsoft.Office.Interop.Excel._Application’. This operation failed because the QueryInterface call on the COM component for the interface with IID ‘{000208D5-0000-0000-C000-000000000046}’ failed due to the following error: Error loading type library/DLL. (Exception from HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY)).

The solution for the above error “Unable to cast COM object of type Microsoft.Office.Interop.Excel.ApplicationClass’ ” is as under:
Go to Control Panel and Use Add Remove programs> Go to the tab Change or remove programs
Go to Microsoft Office Professional Edition 2003. Click the link “Click here for support information”. Use Repair Button.