Transaction type &1 not possible (posting to affiliated company)

What causes this issue?

For the current document, you specified either implicitly (via the
customer/vendor), or explicitly (with a manual entry), that this
posting is to an affiliated company. In this case, Asset Accounting
requires you to use special transaction types. This enables the system
to separately identify such transactions.

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 the line items that you have already entered, and the transaction
type you entered.

Error message extract from SAP system. Copyright SAP SE.