Keyur's comment did give me a clue where to look though.

In Settings / Technical / Actions / Reports the account.invoice object still had a report type of 'webkit'. I set it back to 'pdf' and set the other fields to be the same as in the test database. After restarting the server, the Print button is back!

I run into the same problem after installing report_webkit and invoice_webkit and Openerp v7. The print invoice button disappears for paid invoices.

I managed to solve the problem by adding a button into the view for those states where the print button disappears.

Try this:

- Go to Admin --> UI --> Views (Enable first technical features) and search for "account.invoice.form" view.

- Edit the view and add the below code before closing the header tag </header>

<button name="invoice_print" string="Print" type="object" attrs="{'invisible':['|', ('state', '=', 'open'), ('state', '=', 'draft')]}" groups="base.group_user"/>

Hope this can fix it.

For the Print link in the dropdown I've tried to go to Admin --> Actions --> Reports --> Invoices report and try to re-generate the print button, but it doesn't work.