Error: Found calendar item with inline attachment(s) without corresponding content ID
This error indicates that we are unable to migrate the attachment for the specific calendar item, but the calendar item itself is migrated (without the attachment). This is generally caused by corruption, and is always an issue associated with the Source.
There is no clear resolution for this error. However, enable the Advanced Option Log Subjects of Failed Items to determine which specific items failed; these can be migrated manually.
See How do I get the subject of failed items? for more information.