You may encounter a situation whereby interfaced Cargo contracts:
Do not have the intercompany checkbox checked.
And when trying to save the cargo after checking the Intercompany checkbox throws an error - “I/C Company is missing.”
Since Cargo Mirroring is a process for cargo relet with an internal owner, the cause for this is due the selected company not being an internal company.
To resolve this, you will need to ensure that for both Counterparty and Company entered in Cargo contract, the Internal checkbox should be enabled in the Address book record.