Structure of IDoc type &, object type & is unknown

What causes this issue?

The system tried to read the structure of IDoc type '&v1&', object type
'&v2&'.

System Response

The system did not find the structure definition.

How to fix this error?

Please check the consistency of IDoc type '&v1&' and object type '&v2&'
using the IDoc definition tool.

Error message extract from SAP system. Copyright SAP SE.