Deselect all variants for generic material & first

What causes this issue?

You cannot deselect a generic material if at least one of its variants
is still selected.
When one variant is listed, the whole generic material is always listed
at the same time.
The validity period of the generic material must cover the validity
periods of all its variants.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.