I have realised that payroll_number & shift_type will be duplicated in the employeeshift table but is this the error you are talking about?
OK... I'll tell you (but I thought you'd have more fun discovering it yourself)!
The payroll_number and shift_type are both foreign keys in the EmployeeShift table. Together they make up the primary key of EmployeeShift. You need to go to table design for EmployeeShift, select BOTH FIELDS and then click the Primary Key button. Don't forget to constrain both relationships too as mentioned earlier.
I'd still re-design and observe my design rules if you want a truly wonderful database rather than one that will just do!