When attempting to drag one document from source project and drop it into destination in Strategy Object Manager, the following error message appears:

The requested object with id xxxx and type 22 (Schema) does not exist in the object context
The document has some component transaction report which contains invalid reference to non-existing schema object.
In order to track down the cause of the inconsistency, customers encountering this issue should make note of schema-related changes, Object Migrations, or error messages prior to experiencing the problem. Change Journal, if it has been enabled, can help in preserving this information.
Contact Strategy Technical Support to remove such invalid reference.