if anyone's interested I got to the bottom of this.
Seems the SQL permissions for the user account used for the ODBC DSN had been modified from its original configuration. Consequently the user account didn't have the relevant permissions to the MSDB DB in order to query and disable jobs.
Once the DBAs assigned the correct permissions the migration went through fine.
I also encountered this problem and it has been resolved.
1. View the vcenter system odbc database connection settings and give the database connection account sysadmin permissions.
2. Place migration-assistant programs and folders in the root directory of drive C, not in user configuration files, such as the desktop.
Give yourself the credits you deserve and mark your answer as Correct Answer...
This should be helpful for others who are looking for the same error.