Lets check permissions on the drive and folders and check the owner while we're at it.
Maybe MC is more picky about the permissions on the files it plays than XBMC is.
If you don't care about having permissions for multiple users on the drive (ie, you're the only one whos using the drive) then follow the steps below. If you do have multiple users setup and they have their own folders on that drive, then obviously do not continue! This also asumes your user account is a member of the Administrators group.
The following steps will replace the owner and all permissions on all files and folders with the administrators group:
-right click the drive
-choose security tab
-choose advanced button
-choose owner tab
-click edit (on vista/win7)
-select administrators (plural, 2 puppets)
-tick Replace owner on subcontainers and objects (meaning, all folders and files
)
-click OK
If you get popups about taking full control etc, click Yes. If it can't make the change on an object (error pops up), take note of the file/folder and click continue.
When that is done, click OK (we need to reopen the properties window)
-Right click the drive again
-choose security tab
-Click advanced
-click change permissions
-select administrators or (add) your user name if you're not a member of the administrators group
-click edit
-verify all Allows are checked
-verify that 'Apply to' is set to 'This folder, subfolders and files'
-click OK
-check Replace all child object permissions with inheritable permissions from this object
-Click OK
-Read the warning, choose Yes if you trust me
-if you get an error, take note of the file it mentions and click continue
-click OK
-click OK
If your account is not a member of the Administrators, try that as well. For the above to make sense, you need to be administrator. You probably can't even do this if you're not an administrator but still, check it if you're not sure.
Try playing and importing files again with MC.