The error "Error in initializing the MAPI. Not able to increment reference count to MAPI subsystem" occurs when BDRShield faces difficulties accessing and initializing the MAPI to list and dump Exchange Mailboxes.

To resolve this issue and facilitate the listing, backup, and restoration of Exchange Mailboxes on 64-bit machines, follow these steps:

1. Install Microsoft’s 32-bit MAPI client component by using the "run as administrator" option.

2. Refer to the provided help document for additional information on configuring an Exchange mailbox backup: Configuring Exchange Mailbox Backup 

After completing the above steps, authenticate the BDRShield application with the Exchange server by following these steps:

1. Once the Mailbox is listed in the BDRShield application, attempt to expand the subfolders. If it hangs, proceed to the next step.

2. Access the following URL: http://MACHINENAME:6060/xchangeoptions.sgp?xopt=18. This URL will direct you to create a new MAPI profile by providing the Mailbox profile name and Global catalog Name. Click on save to start recreating the profile, allowing the mailbox to be listed without issues. Afterward, schedule the backup.