You may want to look at the log file to get a better idea as to what might be failing. To do this, close out of all Tableau workbooks, then open just the one you have this problem with. Update the connection or whatever is needed to reproduce the error. Next, go to your c:\<User>\My Documents\My Tableau Repository\Logs folder and open the log.txt file (or whichever log file has the appropriate time stamp) within Notepad.
Once opened, search for the error you received and look on the lines above it. You might discover which part of the SQL statement is bombing out and then concentrate on that area. We discovered an issue with how Tableau was writing SQL query statements using a particular date format; but we would not have noticed it to be able to use an alternative date search if we didn't look at the log file to help us determine what was failing.
Hope this helps,
I followed Andy's instructions and found that I didn't give a Year() function an alias and Tableau needed the column name.
It would be great if Tab could expose the log file errors to us as part of the dialog.