User gets a message stating:

Unable to open your default e-mail folders. The path specified for the file path to PST file is not valid.

This article covers one fix for this issue, if the user does not know where their .PST file is located. Sometimes, the user can even point Outlook to their PST file, and still come up with this error message.

The resolution is to remove the mail profile that is referencing this file. There are two ways of doing this: via the Control panel, or via the Registry. Both should work the same, but I'll cover both methods.

Method 1: The Mail Control Panel
This is the recommended approach. Make sure Outlook is closed while performing this procedure.

• In Windows XP, open the Mail control panel. (Category view users must select "Switch to Classic View" for this option)
• If any profiles are configured, the next window will be your "Mail Setup" screen. Click the "Show Profiles..." button.
• If there is only one profile name listed under "The following profiles are set up on your computer", highlight it, and click the
  "Remove" button. Select YES to confirm your choice to delete the profile.
• The next time the user opens Outlook, they will be asked to create a new profile. Simply pick a name, and proceed with configuration of emaill account usernames, addresses and passwords.

Method 2: Removal via registry keys
Even though the Control Panel is the preferred method, you can remove the settings manually from the registry. Before we proceed, I'd like to refer you to a notice from Microsoft:
...With that out of the way, I'll just say, don't be afraid of getting in the registry. Bottom line: don't be dumb, and delete keys willy-nilly, and you'll be OK.

• Close Outlook by choosing Exit from the File menu.
• Open regedit by Clicking Start -> Run and typing regedit.exe into the box. Click OK to proceed.
• Locate the registry key:
  HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles
  This is where all informatin about the email profiles are stored.
• If this is a default installation of Outlook, it's likely that the only profile listed will be called "Outlook". However, that is not always the case-- each subkey under Profiles details a profile that is set up for the current user.
• Before proceeding, back up the Profiles registry key using the instructions here:
  Export registry subkeys
  Doing this will allow you to revert changes if you do something wrong in this folder. Keep in mind that the worse that could happen is the user has to re-input all of their email usernames, passwords, and default mail servers. No data is going to be lost by this procedure.
• For each folder under Profiles, right click it, and choose Delete. Be sure to choose Yes to confirm you want to delete that key.
• Once all of the keys underneath Profiles are deleted, close Regedit. The computer does not need to be restarted for this.
• The next time the user opens Outlook, they will be asked to create a new profile. Simply pick a name, and proceed with configuration of emaill account usernames, addresses and passwords.

From here, we're running with a "Clean Slate". The user has to configure their email accounts all over again. If you know where their PST file is, you can simply re-import their data into the new profile/PST using these instructions. They're for Outlook 2002, but the procedure didn't change for 2003:

How to back up, to restore, or to move Outlook 2002 data in Outlook 2002

You'd look specifically for the How to Import Personal Folders (.pst) File Data section of the article. Importing the data is pretty straightforward-- if done right, you get all of your notes, appointments, contacts, and email back, just like it was never missing.

Feel free to PM me with any questions regarding this article. Meanwhile, I'm going to close the thread, so it's preserved in an article format, rather than having comments/questions attached to it.