In Outlook Express 6 while putting messages into folders the message:
"Cannot copy Inbox: It is being used by another person or program. Close any
programs that might be using the file and try again."
After the message the hourglass was on screen in excess of 5 minutes. Then completed a system restart. When Outlook Express was reopened the messages in the inbox were gone. Messages from the 1st 4 months of 2006 (which I had unsuccessfully tried to move from another PC 18 months ago) were in the only items in the Inbox.

How can I recover from this?

Hi Beccabuck,

Messages in Inbox or other mail folders disappear

First check the obvious. Click View | Current View and be sure it is set to "Show All Messages". Also verify that "Show replies to my messages" is not checked or you will see only replies to your messages.

If the Current View setting is correct, then the *.dbx file for the problem folder has been damaged or deleted. Older versions of McAfee VirusScan are known to delete OE's *.dbx files if the email or Internet download scan is enabled. You can download a patch on the McAfee web site, or simply disable both the email and Internet download scan modules in VirusScan. These are not necessary to protect your computer if you still have VirusScan running in the background and scanning executable files as they are opened. In fact, the only real reason to use email and download scanning is to make you feel more secure. If this is the cause of your problem, I am sorry to say your messages are irretrievably lost.

In the case of a damaged "Inbox.dbx" file, a new Inbox with the default "Welcome to OE" message will have been created automatically, and will now be using the file "Inbox(1).dbx" or similar. Likewise a new *.dbx file will have been created for any of the "system" folders that are damaged, Drafts, Deleted Items, Outbox and Sent Items. If your default email account is Hotmail or IMAP, the associated files will be named like "Hotmail - Inbox.dbx" or "<IMAP account name> - Inbox.dbx", etc. However the original *.dbx file will still be there, although OE will be unable to display it.

If the damaged *.dbx file still exists, or its temporary version *.dbt, move it to a new empty folder in Windows Explorer. You can then try DBXtract or Macallan Outlook Express Extraction to extract what messages it can.

From: Inside Outlook Express - Errors, Bugs and Problems - Bugs and Workarounds

Hope this helps!
Whiskey14