Conversion from unit & to unit & is not possible

What causes this issue?

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

You cannot convert from unit &V1& to unit &V2&.

System Response

How to fix this error?

INCLUDE NA_SYSAD1
(&V3&, SY-SUBRC = &V4&)

Error message extract from SAP system. Copyright SAP SE.