Cannot read mail messages in OE5

[Vieux Richard]

Could not access the Address Book on a customer’s Outlook Express 5 under
Windows 98. So I backed up his message folders to D: drive & tried to repair it which made no difference. So I chose the option Reinstall previous version of OE. Sadly, this reinstalled from his C: drive, version 4.72. Then I installed my Windows to move him up to 98SE and this installed OE version 5.
It now finds the Store Folder on D: & lists the mail message but will not open any of the folders.