DISM inject drivers into WIM gives error 2

I have just installed a reference windows 7 x64 machine, sysprep-ed it, went into WinPE mode and captured boot.wim image using ImageX.

I then moved the boot.wim to my local PC under c:\wim, and try to inject drivers into it, before I deploy the new boot.wim to other machines. However I got an error 2: Unable to access the image.

The commands I am running are (run as administrator):

Dism /Get-WimInfo /WimFile:c:\wim\boot.wim
DISM /Mount-Wim /wimfile:c:\wim\boot.wim /index:1 /MountDir:c:\mount
Dism /Image:c:\mount /Add-Driver /Driver:c:\drivers\latitude /Recurse

I have successfully injected drivers using DISM to WinPE boot image, using the same steps. So what is wrong?!!! PS: in terms of permissions, I have full-control permission over the boot.wim file and c:\wim folder. Am really puzzled and stuck.. any input is welcome

–update–

I just looked at the log file as suggested by DSIM in the command prompt. It says the Image session has been closed. How come? How can I overcome this problem?

2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Attempting to add the commands from provider: WimManager
2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Succesfully registered commands for the provider: WimManager.
2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Attempting to add the commands from provider: FolderManager
2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Attempting to add the commands from provider: DISM Log Provider
2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Attempting to add the commands from provider: Compatibility Manager
2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Succesfully registered commands for the provider: Compatibility Manager.
2013-05-21 12:27:24, Error                 DISM   DISM.EXE: Failed to access the image folder or image's windows folder.
2013-05-21 12:27:24, Info                  DISM   DISM.EXE: Image session has been closed. Reboot required=no.

–update–

To list the boot.wim info, I run Dsim command and the result seems good:

C:\Windows\system32>Dism /Get-WimInfo /WimFile:c:\wim\boot.wim

Deployment Image Servicing and Management tool
Version: 6.1.7600.16385

Details for image : c:\wim\boot.wim

Index : 1
Name : Win7 Ent64
Description : <undefined>
Size : 14,986,334 bytes

The operation completed successfully.