What causes this issue?

In order to use the integrated creation of master data between Plant
Management and Asset Accounting, you have to assign the fields of the
objects to one another.
Either there is no assignment; or there are assignments, but they have
not been marked as active.

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 your Customizing settings.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.