I am experiencing the same issue. We have pst's located both locally and on a samba network drive. If you move them individually then it will usually work. We often cannot copy calendars for the same reason. They will start copying then it seems to get to attachments within and fail with the error
"Unable to move or copy folders. Can't copy folder. A top-level can't be copied to one of its subfolders. Or, you may not have appropriate permissions for the folder. To check your permissions for the folder, right-click the folder, and then click Properties on the shortcut menu."
The clients I have seen this on thus far all seem to be using Outlook 2003. I still need to try updating the service pack to see if that helps but it seems that the problem has been occurring higher frequencies lately.
Most users had their original PST's created with Office 97, so I have verified the 2gb ANSI limits, ran scanpst.exe, and even created new Unicode pst files with no luck. Any help would be greatly appreciated.