In your code ' Extended Properties=""Excel 12.0;HDR=YES ' of your connection string .a 'Xml' should be added to make ' Extended Properties=""Excel 12.0 Xml;HDR=YES '.
.So you have to modify your connection string as :
ConString = String.Format("Provider=Microsoft.ACE.OLEDB.12.0;Extended Properties=""Excel 12.0 Xml;HDR=Yes"";Data Source=" & ExpFileName)
It seems to be used to specify or validate data in excel sheet .i.e. i am not sure why this is so important but
This connection string works as of your scenario.