Hey Chris - this was a problem in the past with a different data source (Hadoop), and was fixed.
I suspect you already have done this but you should open a support case ASAP.
Question - did this work in PREVIOUS versions? You mention you're using the most current version of Tableau right now...One other suggestion might be to see if the ODBC driver you're using has changed...it looks like a new one was released by the PostgreSQL team last week - I wonder if you need this newer driver and/or are currently using it and need to use an OLDER one?
I also got a little curious and just tried to do this myself with 8.1.5 64-bit - had no problems extracting from a PostgreSQL table with a 4-byte signed integer field. What type of integers are your table?
The extract has worked in the past, although I admit I'm not sure what ver of Tableau last worked. Releases are frequent and I touch this DB rarely.
I am using the latest psqlodbcx64 (09030210). Tried the previous driver (09010200), no luck. Also blew the dust off an older win xp machine with Tab 8.1.4 w/drivers (09010200 x32), Same error.
I tried some variations of table data types. I have one field that is int4, so I eliminated it. Same error. Also tried limiting it to a single varchar field and received same error. Later I tried a mix of varchar and timestamp and got an "EncodeString: Bad argument" error.
Note: this is a postgres connection to Redshift.