Many of our 100~ Outlook 2010 users (all latest updates) get a 'Cannot open mail item' error when searching in Outlook 2010 - The issue only affects mail items in the Exchange 2013 Archive. The issue goes away for a period of time when you close and re-open Outlook.
If you select a mail item in the search results and wait for a few seconds, sometimes we can open the mail item successfully. If you look for the mail items manually in the folder list you can open them no problems.
We found a couple of Outlook hotfixes that claimed to resolve the "Cannot open mail item" error but alas, after a few days the issue has returned. Thankfully not too many people seem to have noticed yet but I've done a spot check test and most users do seem to be affected.
Thanks for any suggestions guys.