Activity start earlier than WBS element & start date

What causes this issue?

The start date that you entered for the activity is earlier than the
start date of the WBS element.

System Response

You cannot adjust the dates from top to bottom.

How to fix this error?

Enter a start date for the activity that is later or the same as the
the start date for the WBS element.

Error message extract from SAP system. Copyright SAP SE.