Unable to Create Standard Promotions because of a Preferred Advanced Promotions Form

Scenario: User is unable to create Standard Promotion, only Advanced Promotions.

The error occurs when any of the Advanced Promotions Form (Buy X, Get Y; Item-based; Order-based) is set as Preferred.
To resolve the error, mark the Standard Promotion Code Form as Preferred
 
1. Navigate to Customization > Forms >  Entry Forms.
2. Locate Standard Promotion Code Form > mark as Preferred.
3. Click Submit.

NOTE: Applies to Advanced Promotions v2.0 and above (Bundle ID 31356).