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What causes this issue?

You want to plan the field group "Total price" manually and the field
group "Planned activity" automatically (or vice versa) using these
planning parameters.
The result of planned activity multiplied by total price are the costs
with which the cost center is credited in the plan. This means that
you have to take both field groups into account when you are planning,
since the secondary costs are changed both by the planned activity and
the total price.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Please flag both field groups, or
unmark both.

Error message extract from SAP system. Copyright SAP SE.