Hi,
Thank your for posting your query,
Final Error Description: "Access is denied to Remote Agent. Check the login account for the specified device. "
As it's not clearly mentioned that whether you are trying to take the backup of Information store, indivisiual mailbox box backup or the mailbox store.
Please follow these steps to work on this issue..
1-Set new mailbox for Backup Exec with domain rights/exchage rights.
2-Activated account by sending and receiving a message to it.
3-Made new account the System Logon Account.
4-Enabled Restric Anonymous Support.
Document ID: 238618
5-Recycled the Backup Exec Services and the Remote Agent service.
6-Ok to close.
If getting the problem again then please reply back with more details.
We hope this information helps, if you have any other questions please respond to the post and we will be more than happy to assist you further.
Rega