Error message working offline on new domain/username with old exchange server

Our company is migrating to a new domain. One of the users gets the following error message when trying to send an email whlist working offline;
Microsoft Exchange server - Sending reported error (0x80070005) You don't have approprite permission to perform this operation

More details that may be relevant;
1. The user is attaching to the email server on the old domain though the new domain is a trusted domain
2. The migrated user had a temporary username on the new domain which has now been renamed to a new username
3. No other migrated user has this problem working offline
4. We have tried deleting the offline ost file in case it was corruptedStart Free Trial