Birst has their own built driver for Tableau (or they used to in 2015). Are you using their driver or the ODBC driver for Tableau?
One caution: Other Databases (ODBC) - Tableau
I would read that page and make sure you follow the advice there. The ODBC connector needs to be tweaked and it could be Birst and Tableau are not compatible when using that generic driver. Let me know which driver you used.