DDIC structure & not available for unit determination! (TMC6)

What causes this issue?

The system could not find the reference table &V1& in the Data
Dictionary while it was determining the units for your communication
structure.
This situation can occur if you manually delete communication
structures, but the corresponding LIS inbound interface continues to
exist.

System Response

Generation will continue; the error will have no direct effect on the
generation of your structure.

How to fix this error?

It is imperative that you correct this error.
The information structure / updating cannot otherwise be generated.
The where-used list (under "Utilities") helps you to display the LIS
inbound interface for an incorrect structure.
You can then delete the incorrect LIS inbound interface.

Error message extract from SAP system. Copyright SAP SE.