The forecast date must lie within the current or following period

What causes this issue?

A forecast can only be carried out for either the current period or for
the following period. The date that you have entered, however, does not
lie in either of these periods.

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?

Enter a date that lies within these two periods.

Error message extract from SAP system. Copyright SAP SE.