Diagnosis
You want to assign participating settlement units on &v1&. However,this valid-from date is not the period start of the current mastersettlement unit since it has the settlement variant &v2&. One exampleof a valid period start date is &v3&.

Procedure
Enter a valid-from date for the assignment of other participatingsettlement units that is also the start of the settlement period forthe master settlement unit. You can only make an assignment for theperiod start date of the settlement variant.