I'm loading Jive Analytics Data into BigQuery, and I get Integers like the below for in a field called ActivityTime.

These are actually milliseconds since 1970/1/1, so I create a calculated field in Tableau like:

DATEADD('hour',-8,(Date("1/1/1970") + (([ActivityTime]/1000)/86400)))

This works fine against a CSV dump of the data, but when I connect to BigQuery it returns nulls.

Then I decided to go to Data Source and create a Custom SQL source for the data as follows:

SELECT MSEC_TO_TIMESTAMP(ActivityTime) fromUnixTimeStamp, * FROM ExpressDS.express_activity

It appears the work.  But then when I press on Update Now I get an error:

Field 'ActorActionObject_Created' not found.

Any help with this would be much appreciated.