I have a Mailbox that 10k+ folders and is 15+ GB. I'm having trouble moving it to another mailbox database so I thought I could export it to a PST just to have a backup copy in case things went south.  

I issued a New-MailboxExportRequest and the process ran through to 100% then started over.  Now it is Stuck at 10%.

There is a PST file on the share but it is locked by Exchange so I cannot verify the data is valid.

When run Get-MailboxExportRequest | Remove-MailboxExportRequest I get 

Failed to communicate with the mailbox database.
    + CategoryInfo          : ResourceUnavailable: (0:Int32) [Remove-MailboxExportRequest], MessageSubmissionExceededException
    + FullyQualifiedErrorId : 1B35C29F,Microsoft.Exchange.Management.RecipientTasks.RemoveMailboxExportRequest

Does anyone have any recommendations to remove this Export Request and release the file

Have a look on this earlier discussed thread that might helps you - New-MailboxExportRequest doesn't function anymore

Removing mailbox export and import requests: http://thoughtsofanidlemind.com/2010/12/21/removing-mailbox-export-and-import-requests/

Using the Exchange 2010 Mailbox Export features for Mass Exports to PST files: http://new.netct.in/more/1756767_4/Using-the-Exchange-2010-Mailbox-Export.html

You may also take help from this programmed application i.e. import/export solution which lets you to accomplish this task without any interruption.

Hope it helps you!