1. Go to Administer CiviCRM | Global Settings | Payment Processors and to the new payment processor screen.
2. Select the default, 'empty' (- select -) payment processor.
The page tries to reload with the processor-specific fields, but fails with an error.
The fix should be that either this does not throw an error (empty set of fields?) or (better?) do not provide the default '- select -' selection at all.