Reset Message class of imported emails?

[Brewder]

Hello,

I'm moving a family member from Windows Live Mail to Outlook/Office 365.  I exported the mail from WLM into Outlook 2007.  Then exported that to a PST and imported it to Outlook 2016.

The problem is now every single one of the 3,000+ messages, generates this pop-up when you click on it:

The custom form cannot be opened.  Outlook will use an Outlook form instead.  The object could not be found.

I only get this error on imported emails.  New ones are fine.  When I turn on the Message Class in the view for the inbox, messages that generate the pop-up have the Message Class ???? and everything that is new of course is IPM.Note

How can I fix all of my imported messages to get rid of that annoying pop-up?  I sync'd the mailbox (IMAP) with gmail... then deleted my outlook profile and let it pull the mail box down from scratch thinking that would reset the message class, but I didn't.  I'm at wits end!

//Brew

[#2]

@Brewder what kind of account was setup in WLM, and who is the provider?  What kind of account did you export to in Outlook 2007 and who is the provider for it?  It is generally better to use File > Open and Export > Open Outlook Data File than it is to import the .PST.  If you open this .PST in Outlook 2016, what do the messages look like?