Esh - the answer comes in two parts:

1) Deleting invoices when finalised - not possible - so you don't have to worry about blocking people from doing so.  ie once the transaction (invoice, credit, payment etc) is finalised one cannot change or delete it.

2) Deleting invoices when not finalised - possible if you have the required authority. Go read http://www.openvpms.org/documentation/csh/1.7/concepts/users - specifically the Roles and Authorities part.

You should come to understand that the authorities define whether you can create/save/remove a given 'thing' (actually an 'archetype' - see http://www.openvpms.org/documentation/csh/1.7/admin/archetype).

In our system we define a number of 'Roles', Base, Logistics, and Administrator.

The Base role is given to everyone - it allows them to do most of the standard things - below is the first of 5 pages of Authorities in the Base Role:

Notice that for a number of authorities (eg Customer Account Act) there is a Create and a Save - but no Remove.  The lack of the Remove blocks a user with the Base Role from deleting an invoice.

You will also see that the Base role includes the full Create, Remove, Save set for Contacts - ie a Base person can delete a contact.

Below is the setting for the Administrator role. As you can see an administrator can create, remove, save everything.

Below is the Logistics role. As you can see they can  remove products, prices, suppliers etc - ie all whats needed by logistics people.

So back to the original question: how to stop someone deleting a non-finalised invoice?

Answer: make sure that thay have a role which does NOT include the  'Customer Account Act Remove' authority

Regards, Tim G