Invalid input combination

What causes this issue?

The input combination of special stock indicators "&V1&" (FRM...) and "
&V2&" (TO...) is not valid.

System Response

The system checks the following input combinations:
Field "Special stock FRM" = all valid values -> field "Special stock
TO" = " " (blank)
Field "Special stock FRM" = " " -> field "Special stock TO" = all valid
values
The two fields must have different values.

How to fix this error?

Enter a valid field combination.

Error message extract from SAP system. Copyright SAP SE.