I know it is a silly question, but do you have the SAP GUI installed locally on your PC?
I have, and was able to connect and do some charts with Tableau against our production instance of SAP BW 7.0, but I am now trying to connect with Tableau 8.1 Beta and getting a similar error. It worked fine with 8.0, but not 8.1.
Same problem here.
If you have only installed the SAP GUI, install the 32-bit version of Tableau. If you wish to use the 64-bit version of Tableau, you will have to also install the BW ODBO driver.
I had the same problem with Tableau version 10.2 and after a lot of investigation and with the help of Tableau Support I figured out that the connection to SAP BW works only with the ODBO BW driver version 7.3. I had the ODBO BW driver version 7.4 and this is not working.
So the solution would be to us use SAP ODBO BW driver version 7.3.