An error occurred when calculating maintenance plan &1

What causes this issue?

As maintenance plan &V1& was being calculated, the following error
occurred:
You are calculating this maintenance plan in the time period from &V2&
to &V3&. The package that is being used in this time period for
scheduling, &V4&, no longer exists in the current maintenance task list
that was assigned in the maintenance item and therefore cannot be
calculated. The package was either deleted or included in another
maintenance task list that does not use this package.

System Response

The system cannot carry out calculations. As of Release 4.6C (or as of
Release 4.0 with note 186734), when the system calculates maintenance
plans, it takes into account the existing maintenance calls in the
database, therefore including the package that is based on this
appointment. If there is no such package for the point in time in which
the calculation for the valid maintenance task list is made,
calculation is terminated.

How to fix this error?

Make the calculations for maintenance plan &V1& in a time period in
which only the packages that are currently valid (current maintenance
task list in the maintenance item) result in appointments.

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.