See if this link helps you. I think you might just be miss-typing the syntax a little.
Specifying the view, workbook, or data to export: You specify this using the
"workbook/view"string as it appears in the URL for the workbook or view, not using its “friendly name,” and excluding the
:iid=<n>session ID at the end of the URL. For example, to export the Tableau sample view Investment Growth from the Finance workbook, you would use the string
Finance/Investment Growth, or
-t <site_id>if the server is running multiple sites and the view or workbook is on a site other than Default.
To export a workbook, you still include a valid view in the string you use. Using the above example, to export the Financeworkbook, you would use the string
Finance/InvestmentGrowth. Finally, to export a workbook, it must have been published with Show Sheets as Tabs selected in the Tableau Desktop Publish dialog box.
Hi Mandar, Did you manage to resolve this issue? I am having the same issue if you could let me know how you got around it it would be great. Thanks a lot