Characteristic with confirmation number & is already blocked

What causes this issue?

The results for the inspection characteristic with confirmation
number &V1& were not accepted because the inspection characteristic is
already blocked in another transaction.

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?

Make sure the result confirmation is sent over the IDI interface
or over the confirmation transaction that is blocking the inspection
characteristic.

Error message extract from SAP system. Copyright SAP SE.