What causes this issue?

For unit-of-production depreciation, the system determined the number
of units based on the previously used number &V1&. The &V2& units
that you entered for depreciation key &V3& differs from this number.

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?

Check if this variance is allowed. It could be the result of
multiple-shift use or shutdown.
If necessary, correct the defined number of units for the
unit-of-production depreciation key &V3&.

Error message extract from SAP system. Copyright SAP SE.