EDIT: No... bad call on my part... Turned out to be Windows 10 and an Exam Diff Pro install (version 6.x) that was causing problems.
Solved it by removing Exam Diff pro, restarting Windows explorer and restarting outlook a few times for things to right themselves...
Original post:
I suspect this is an Avast issue given previous problems but the symptoms on this problem are as follow:
Using Outlook 2013 all day then notice that after around 15:30 BST, emails are no longer showing up in the preview window. Wait to see if it's just the system processing then try opening an email as a pop-out window.
No joy.
Restart Outlook and find that it will no longer run. Similarly Word 2013 is now having problems starting properly.
Disable Avast and find that Outlook will no longer simply crash but will start up. Word also starts working. Excel not affected.
Given the previous experience with Avast blocking Office 2013 I suspect a recent live update from Avast is responsible and will confirm tomorrow as now on Dad duty.
