I created a new database (clean install) and started to add products. I had fun and games trying to get a discount value to be accepted. I finally realised that the problem was that when there are no records in the discount table, the 'add product' page does not have the drop down allowing discount type to be set. I manually created a record in the product_discount table and then it was fine. Perhaps the install script should add a zero discount record to the table at install time just to get the ball rolling?
Regards
Phil