this may help
Description:
SYMPTOMS
Customer receives the following error when opening OE 4.0 or 5.0: Outlook Express could not be started because msoe .dll could not be loaded.
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CAUSE
This issue can occur if the customer uninstalled Microsoft Internet Explorer 5, and then reinstalled Windows 98 to restore Internet Explorer 4.x. When this is done, Outlook Express 5 is not uninstalled and customer can end up with mixed versions.
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Solution:
RESOLUTION
To resolve this issue:
Use Registry Editor to view the following registry key: KEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Setup\Migration Delete the 100 subkey folder if it exists, and then quit Registry Editor.
Click Start | Settings | Control Panel.
Double-click Add-Remove Programs.
Click the Install/Uninstall tab.
Click to select the Microsoft Outlook Express 5 check box, and then click the Add/Remove button.
When customers receive this message, Uninstall requires at least Internet Explorer 5 to work correctly. If you continue, setup may not be able to restore the previous version of this application. Do you want to continue?, click Yes, click Yes to continue, and then click Yes to restart your computer.
Click Start | Settings | Control Panel.
Double-click Add-Remove Programs.
On the Windows Setup tab, click to select the Microsoft Outlook Express check box, and then click Apply.
Insert the Windows 98 CD-ROM when prompted, click OK, and then click Ok.
This information is referenced from Microsoft Knowledge Base article Q232480.