What causes this issue?

The prerequisite plan &V1& and the dependent plan &V2& do not belong to
the same archiving subobject.

System Response

The system does not allow the prerequisite plan &V1& to be destroyed.

How to fix this error?

Assign the dependent plan &V2& and the prerequisite plan &V1& to the
same archiving subobject.
<ZH>Example</>
<LB>MED</> is the prerequisite plan for <LB>DENT</>.
<LB>DENT</> belongs to the archiving subobject <LB>A_1</>.
<LB>MED1</> belongs to the archiving subobject <LB>A_2</>.
To be able to destroy both plans together, <LB>DENT</> and <LB>MED1</>
must both be assigned to either the archiving subobject <LB>A_1</> or
the archiving subobject <LB>A_2</>.

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.