Type conflict in join &-& = &-&

What causes this issue?

Two fields with different data types or lengths are elements of a join.
Such conditions normally do not make sense.

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

System Response

This is only a warning message.

How to fix this error?

Check in your own developments whether the join condition was defined
in this way on purpose.

Error message extract from SAP system. Copyright SAP SE.