I'm going to take a guess that this workbook was published without an extract, that it's either a live connection or using a file-based source and the file was included when published. You'll be able to tell that by opening the workbook in Tableau Desktop.
Thanks for reply, Yes I have used the live connection as well as exported the data source (in this case data source is a SAP BW query). I am new to tableau, All i was trying to do is to create a schedule and schedule an extract. I was able to create a schedule with out any issue but I am unable to use the schedule or in other words use schedule a refresh extract. Is there something i am missing?