The changes are posted under number &

What causes this issue?

Your planning changes have been made. After update, these changes can
be used for further evaluations. Each change you make is documented by
means of plan line items. This change was updated under the above
number and can be displayed later.

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?

Error message extract from SAP system. Copyright SAP SE.