Mailbox Migration Error O365 P Plan Cutover

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I've setup a new tenant on an O365 P Plan and am in the middle of a cutover migration.


I've migrated several mailboxes but I had 3 that errored with the following issue:


Unable to load DLL 'WMVCore.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)


Two of them I was able to simply delete as they were test mailboxes, however I also have the issue with my own mailbox.


So any ideas?




All Replies
  • Hello Nathan,

    Thank you for your post.

    As I understand, you failed to migrate three mailboxes with cutover migration and got the following error.

    "Unable to load DLL 'WMVCore.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)"
    Before going further, could you let us know if you have enabled the unified messaging (UM) feature for your on-premise mailbox?

    Based on my experience, this problem can occur when trying to migrate a UM enabled mailbox with cutover migration or staged migration.

    For this situation, I would provide you with two suggestions.

    Suggestion 1
    If you just want to move emails in the last three mailboxes to Office 365, you can refer to detailed steps to move these data by exporting/importing .pst file.

    Use Outlook to Move Data Between Accounts

    Suggestion 2
    If you still want to migrate the last three mailboxes with cutover migration, please refer to steps below to do it.

    1. Disable the UM feature for all UM enabled mailboxes.

    2. Remove all mailboxes migrated to Office 365.

    3. Follow instructions in article below to migrate mailboxes with cutover migration again.

       Migrate All Mailboxes to the Cloud with a Cutover Exchange Migration

    Thank you.
    Jack Sun

  • Hi,

    Thanks for the response. Two of the mailboxes were test boxes, so I deleted them. However the other, is my primary mailbox.

    It used to have UM enabled and also an archive, however it no longer does. This was disabled a while ago and the UM role removed from the server.

    I would be very keen to get this working as I don't want to resort to a PST migration.

    Any other ideas?



  • Hi Nathan,

    Thank you for your update.

    If you want to continue migrating emails for your mailbox with cutover migration, please try the following steps.

    1. Double confirm that you have disabled the UM and archive features on your on-premise mailbox first.

    Plan to Migrate UM-Enabled Mailboxes

    2. Remove all mailbox migrated to cloud from Office 365 and do a new cutover migration with steps in artice Migrate All Mailboxes to the Cloud with a Cutover Exchange Migration.

    If the issue persists, please connect the windows powershell to Exchange Online and run the cmdlets below, and then post back the result.

    Get-MailboxStatistics username -includemovehistory | fl

    Thank you.
    Jack Sun

  • Hi,Thanks, so the archive and the UM is definitely disabled on the mailbox in question. I have removed all my users from O365 (except my serviceadmin user) and I have kicked off a new cutover migration batch.This has failed again in the same way on the same mailbox.So here is the Get-MigrationStatus:

    RunspaceId                  : 200a9073-1db6-4072-824f-8c3d5591936d

    Identity                    : 90DA65B9-2154-4338-A690-602DF1FD5BAC

    ServicePlan                 : BPOS_L_E14_R5_Slim

    Status                      : BatchActive

    MigrationInProgressSince    :

    MigrationInProgressSinceUTC :

    TotalCount                  : Mailboxes - 7, Groups - 2, Contacts - 2

    SyncedCount                 : Mailboxes - 5, Groups - 2, Contacts - 2

    ActiveCount                 : Mailboxes - 1

    ProvisionedCount            : Mailboxes - 6, Contacts - 2

    FinalizedCount              : None

    MigrationErrorsCount        : Mailboxes - 1

    LimitErrorsTo               : 500

    MigrationErrors             : {, Error:Unable to load DLL 'WMVCore.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)}

    NotificationEmails          : {}

    MigrationType               : Exchange

    CanSubmitNewBatch           : False

    SuccessReportUrl            :

    ErrorReportUrl              :

    IsStaged                    : False

    Config                      : Maximum current migrations per time:50; Maximum number of batches:1; Migration Features enabled:None

    IsValid                     : True

    Here is the output from Get-MailboxStatistics nathan -includemovehistory |fl

    PS C:\Users\administrator.MSEXCHANGELAB> Get-o365MailboxStatistics nathan -includemovehistory |fl

    WARNING: The user hasn't logged on to mailbox 'nathan' ('19ef1e1d-9a37-4eb1-a971-012a9a1a0152'), so there is no data to return. After the user logs on, this warning will no longer appear.

    Thanks for your continued support.



  • Hi,

    Any updates on this please?



  • Hi Nathan,

    It appears that the mailbox is still enabled for UM or still has the properties for UM. You can try to change this using PowerShell:

    Disable-UMMailbox -Identity -KeepProperties $false

    This may or may not work, since the role has already been removed. If it doens't work the last option may be to do a .pst migration of that mailbox.


  • Was having exactly the same problem, in almost exactly the same scenario - got the WMVCore.dll error, disabled UM for the 2 problem accounts, but still the same error.  I was able to resolve this in my particular instance, by clearing the "msExchUMSpokenName" attribute in AD for the problem accounts using ADSIedit.msc.

    Just open up ADSIedit.msc, find the problem user(s) CN (mine were under Default naming context -> DC=xxxx,DC=yyyy -> CN=Users -> CN=Username).  Highlight the username, and right click.  Go to "Properties" and scroll down in the Attribute Editor until you find msExchUMSpokenName.  If it has something in there, double-click on the value and then hit "Clear" and "OK".

    The changes are instantaneous, so you should be able to try and re-migrate immediately.

    Of this isn't the value causing problems, you may have to clear other values as well.  Try comparing all the msExchUM* values with another user's values that you were able to successfully migrate.

    I hope this helps!