i have following error with tableau to SSAS connectivity

An error occurred while communicating with the Microsoft Analysis Services data source 'USERNAME'.

The drivers required to connect to the data source are not installed. The error may need to be resolved through local configuration changes on the Tableau side. The drivers necessary to connect to this database are not properly installed. Visit http://www.tableau.com/drivers to download driver setup files. Database error 0x80040154: Class not registered Unable to connect to the server. Check that the server is running and that you have access privileges to the requested database.