Referenced activity does not exist

What causes this issue?

Why is it relevant?
Every demand for an installation kit should be assigned to a network
activity to define the sequence in which installation kits shall be
assembled
Possible Reasons:
This could be a bug in the bill of material transfer (transaction CN33,
CN33_N) or in the deletion of a network activity

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?

Fix:
Re-explode the current BOM version either in this app or using
transaction CN33_N

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.