SOM will not let you save a new Quote unless all the required fields are filled out.
Sometimes, it may look to you like they are, but the Save button still doesn't enable.
The #1 cause of this is the Customer Field. When you begin to type a customer name in this field, it will show you suggestions from Core's database. You must select one of those from the list. If you just keep typing, the list of customer matches from the database will eventually go away. It will look like you have a valid customer name in the field, but you do not. You need to select a customer from the list, than the Core Customer ID can be saved.
The next most common cause of this is that your Design Required or PM Required checkboxes are checked, but you have not selected a Designer or PM. Either select one, or uncheck the appropriate checkbox.