Account Quotation wizard; may fail with the error "Primary Key does not exist in collection."

The Account Quotation wizard may fail with the error "Primary Key does not exist in collection." when using the Promotions Add-On.

To recreate:

1. Open the Account Quotation form.
2. Select an Account Type with Promotions.
3. Select a Promotion.
4. Click Next.
5. Click Back.
6. Change the Account Type.