Error - Object reference not set to an instance of an object

I recently created a new connection to a Postgresql database. I am using the PostgreSQL ANSI(x64) driver and have Toad Data Point version 5.4.0.360 (64 bit).

I am unable to run any queries of tables without getting a 'Object reference not set to an instance of an object.' error. I can see data if I open a Viewer window on a table and click the data tab but selecting from the table gives the error.

5.4 is a pretty old release. Since then, there's been quite a few enhancements and fixes.
I'd suggest upgrading to the latest 6.1 release and seeing if that fixes your issue.