Start date was set to earliest calendar date

What causes this issue?

You have selected a start date which is before the start date of at
least one relevant calendar.

System Response

Every calendar has an earliest start date. The system selects the
latest from all the earliest start dates and sets the selected start
date to this date.

How to fix this error?

Accept the system's selection or choose a later, suitable date.
Alternatively you can edit the calendar or calendars for the period you
require.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.