42501: INSUFFICIENT PRIVILEGE ERROR while querying in Postgresql

It simply means that you have no permission to access app table. Request your root or database administrator to grant you the permission to access app table. if your are the root or have granting privilege you can use grant command to grant your self permission to use all sql statements on table or database
For Example:

               grant all privileges on database money to cashier;

before that you have to login as root or user that have granting privileges
for more details on this command refer to http://www.postgresql.org/docs/8.1/static/sql-grant.html

The user running the query will need permissions to that table. You can grant them to that user with the GRANT statement. The below is an example that grants to PUBLIC

GRANT SELECT ON tablename TO PUBLIC;

Also I have seen SELinux cause isses and places such as here mention it. I am not exactly sure of the command to turn SELinux off but you can see if it is running by using

selinuxenabled && echo enabled || echo disabled