Check the use of instruction &.

What causes this issue?

The
<DS:DE.PLAVO>instruction</> for planning delivery schedule may still be
used in items in sales scheduling agreements.

System Response

Once deleted, a planning delivery schedule instruction becomes invalid
in <ZH>all</> sales scheduling agreements. This means that you can no
longer maintain forecast, just-in-time (JIT), or planning delivery
schedules in sales scheduling agreement items that still contain this
instruction.
Also, when you make changes to such a sales scheduling agreement,
schedule lines in the planning delivery schedule lose their relevance
for planning and delivery. Schedule lines in the forecast delivery
schedule replace them in this regard.

How to fix this error?

To ensure consistent data, we strongly recommend that before deleting
this instruction, you remove it from <ZH>all</> sales scheduling
agreements that use it.

Error message extract from SAP system. Copyright SAP SE.