CPUU fails with "[Error] Cannot open default message store. MAPI error. Error code" (22161)

CPUU fails, the last logged error is:

"AM Core [Error] Cannot open default message store."
MAPI error.
Error code: 0x80040113
Description: MAPI_E_USER_CANCEL

Often the issue is caused by name resolution or when the (target) Exchange Server is not accessible from user's workstation.

Verify both the source and target Exchange servers can be reached by PING and by NETBIOS NAME.

In some rare cases CPUU is executed from users log on script before users workstation has mapped all required drives (when some PST files are stored on mapped drives) or before network connectivity has been completely established, eg. another script which populates the host file or updates another information has been executed.

If this is the case, it is a good idea to configure CPUU to be executed as last in the logon script and eg. if another commands or mapped drives are involved it might be a good idea to put a 10-30 second pause before the CPUU starts. This will ensure that all the required files are available at the time of running the utility.

It has been confirmed that this issue might also arise when users profile contains many mailboxes, in this case it is a good idea to remove additional (unnecessary) mailboxes from outlook profile.

In some cases this error is logged when another MAPI program is running and accessing the mailbox.
This could be any software which accesses the users mailbox (eg. Outlook or Blackberry on another WS) and this can cause the MAPI_E_USER_CANCEL error.