I am not crossing databases so I don't understand what is causing this error.

Its a message from your ODBC driver (not perl module)

So i'd try to be more specific like you are here   db_name.user.table_name and use "full" names like that for all the names in your statement

Then I'd check the permissions your user has, these links talk about this permissions issue http://colbran.co.za/wordpress/netezza/netezza-schemas-and-cross-database-access/, http://netezza-tutorials.blogspot.com/2011/03/accessing-other-databases.html

Then the drastic options is looking for a different ODBC driver ... or even worse, different database system