Record type & unknown

What causes this issue?

The system tried to read the structure of IDoc record type '&v1&'.

System Response

Record type '&v1&' is unknown.

How to fix this error?

Known record types are:
Control record, 'C'
Data record, 'D'
Status record, 'S'
Please check the required record type.

Error message extract from SAP system. Copyright SAP SE.