Yesterday I was working with the Migration Wizard and ran into this error. It took me a couple of steps to verify my settings before I was able successfully bypass this error and continue migration. I wrote this guide to help you guys to move on in this situation.
As you know the Migration Wizard can run in UI and in command line mode. There are fewer chances that you will get this error in UI mode that is why I will concentrate more on running the Wizard in command line mode. So don’t panic, here are the steps I recommend to follow if you come across this error:
a. Start with checking the permissions of the account you use to run the Migration Wizard. Account running Migration Wizard must be a target domain account. Make sure this account is a member of the target domain admin group. Migration Wizard need these permissions for various R/W operations across the target forest while matching on user object and cleaning contacts(next time I will go through the Migration Wizard matching criteria).
b. Make sure that the account you specify with "/a:" option has admin rights on the source mail system. If you perform migration from Exchange verify that this account also has Full Exchange Administrator rights delegated in the source Exchange org. To delegate the role use Exchange Administration Delegation Wizard from ESM.
c. If your source is Exchange 55 server you will need Service Account Admin rights delegated to this account. Use Exchange 55 Admin to delegate this role.
d. Next, check the command line string you entered. Make sure that your "/a:" option is correct. If your source is the Exchange server, make sure that you entered this value in the "<domain>\< account>" format.
e. You can skip the "<domain>" part if you entered it in control file with the "Postoffice" key: "<domain>\<exchange server>". With Exchange 2003 SP1 you no longer need to expose password, just use the "/p:*" option.
f. Next check your control file. Make sure you entered the value for "ExchStoreDN" key correctly. This key as well as the "Container" key requires FQDN of the store where you want the mailbox to be created. I always use LDP to get these values for the control file. If the target Exchange org has plane structure with one storage group you can use "ExchStore" key assigning cn of mailbox store to it.
g. Also, if this error appears while using command line, to help find the cause, you may switch to the Wizard in UI mode and go from screen to screen. If it works in UI mode check the key values in the control file and the command line string.
Hope after all these steps you can successfully bypass this error and start the migration process. But if you still have it, please let me know and I will help you.