What causes this issue?

Planned order number &V1& cannot be completely converted because the
dependent planned order no. &V4& no longer exists.

System Response

The conversion is terminated.

How to fix this error?

You should carry out an MRP run for the material &V2& in plant &V3&
so as to achieve consistent data. In MRP use planning mode "3":
'reset planning data'.

Error message extract from SAP system. Copyright SAP SE.