That might be because of credentials.
Please check the below requirements for the account that you are using to restore
1> the account should be unique(first five character shuld be unique)
2> should have active mailbox
3> should be unhidden from GAL
4> Should be domain admin
5> should have full delegation to exchange
also click on network - logon account -> and make sure you have the system logon account and should have the correct credentials for it