When you "View Underlying Data", Tableau will send a query to OBIEE via BI connector with all the columns in the Worksheet Panel from where you drag and drop into the worksheet.. It so happens that some times one or more of the columns in that Table are not defined correctly in OBIEE. So, OBIEE will return an error.
In the dashboard that you have, check if the Table/folder has an issue with one or more columns in the underlying RPD. Please investigate which column/s has the issue? You can check the BI connector log file and identify the column/s which has the error. The error will be in the form of an XML error message from OBIEE. The error will typically show an error with a column in a OBIEE folder/table.
You can hide/remove those problematic columns from Worksheet and try View Underlying data. It will work fine.
If this approach doesn't solve the problem, please contact us at firstname.lastname@example.org and send us your log file.