Two possibilities exist:

1. You may have forgotten to create the employee type. Press Assumptions/Costs/Personnel/Employees, and add a new employee type that you want to use to drive sales.

2. You may have included the employee type but failed to allocate it to marketing and sales. Press Assumptions/Costs/Personnel/Employees; select the employee type in question; change the 'Salary Charged to' field to 'Marketing and Sales.'

Related Questions:

How do I add or change employees? / How do I add or change personnel?

How do I change the department or division I charge an employee salary to?