Hello Timothy,
you should have a look to the security settings of the user you want to migrate (compare security settings of user account with settings for a account which could be migrated). Within Domain Prep of OCS R2 there where special rights created on the Domain OUs (Groups RTC* get a few rights). Normally, if inheritance is enabled, this security settings should be applied to all Accounts. If inheritance is not enabled, the needed rights are may be missing, so there is a permission issue for migration.
regards
Gerhard