When you take a look on our community site, you will find that this error is usually generated when either the source or destination target does not exist. António went even further with this, and was so kind as to provide an explanation.
It turned out that the MigrationWiz EWS (Exchange Web Servers) queries will fail if the mailbox is hidden from the Global Address List. When the mailbox is hidden from the GAL, he above error message will be thrown during the migration. To solve this issue, António correctly says to disable the “hide from Global Address List” option on the mailbox you’re migrating.