Struggle of finding regarding the meaningful info

Hi,
My creation of a PST at main drive c:pstfilesuser.pst to test importing PSTs into Exchange 2010 via PowerShell.
I got the installation of 64bit outlook in server, and also do adding “import export roles” to the account I used before.
Then I started the use of the command ‘Import – Mailbox – Identity (Username) – PSTFolderPath
c:pstfilesuser.pst’ to import the PST file into (username)’s mailbox.
And hit the following error:
Error was found for XXX because: Error occurred in the step: Approving object. An unknown error has occurred., error code: -2147221219 + CategoryInfo : InvalidOperation: (0:Int32) [Import-Mailbox], RecipientTaskException + FullyQualifiedErrorId : CFFD629B,Microsoft.Exchange.Management.RecipientTasks.ImportMailbox
Could you please help me out to know what is going on here?
Thank you in advance for your help.
