stops the processing of the remaining items in that class.
Looking at my record of a previous troublesome migration, here's what I wrote at the time:
"The owner was set to John Smith, whose AD account had been deleted so the SID mapped to a blank entry. When the Import was run the blank entries caused an error and the item import to fail, some of which were folder items, some collections, some programs and some command lines. When a command line import failed none of the following command lines in the Import Package were processed, even ones with valid Owner names.
The old SID was replaced in the dbo.security.trustee table with a SID of a new, dummy, user."