Error in transformation rule &1

What causes this issue?

The function module 'EWC_CONT_TRANSFORM' terminates because it has
ascertained an error in the transformation rules.
This involves the following error:
&V1&
The rule with the target element '&V2&' / key field '&V3&' is affected.

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?

Transfer the correct transformation rules.

Error message extract from SAP system. Copyright SAP SE.