Action was canceled in customer exit

What causes this issue?

Matchcode IDs and views belong to the same name range. As a result, the
complete name range occupied by matchcode IDs are locked for matchcode
objects. No 5-place view names may exist whose first 4 places
correspond to those of a matchcode object.

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?

Error message extract from SAP system. Copyright SAP SE.