Sample &1 for characteristic w/confirmation no. &2 is not valid

What causes this issue?

The desired activity could not be carried out because the sample &V1&
for the inspection characteristic with the confirmation number &V2& is
not valid.
A partial sample can be marked as being invalid on the basis of its
attribute.

How to fix this error?

Make sure you really want to carry out the activity for the partial
sample &V1&. If so, you must designate the sample as being valid on the
basis of the attribute.

Error message extract from SAP system. Copyright SAP SE.