hstore type does not exist with hstore installed postgresql
For anyone that runs into this question. I ran into this problem today and found a solution.

Depending on where you have the extension installed, it may not be in your search_path.
In my case, i had it installed into the schema 'shared_extensions' on the same db.

using SHOW search_path displayed $user, public, which means that it was never looking in shared_extensions for the extension and it's operator

To fix it run
SET search_path TO "$user", public, 
followed by the schema where the extension is installed.

Hope that helps!