New package number &1 already exists and has phase &2

What causes this issue?

You tried to restart the runtime forecast and to reuse a package number
already created.

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?

If you want to restart the runtime forecast, the action is continued.
If you want to create a new package, choose a package number which you
have not yet assigned or delete the package first.

Error message extract from SAP system. Copyright SAP SE.