Since we've updated our machines from Windows 7 to Windows 8 and upgraded from Office 2011 to Office 2013, there are some users that have a non-functioning "Add-->Email" button on the ribbon (Opportunity, Account, Contact, etc).
This only happens in CRM for Outlook (and only when you have setup "E-Mail" as the CRM for Outlook window).
When users try to add an email to their opportunity, and click the "Add-->Email" button, nothing happens, or the popup remains in the background and it is very hard to find.
Only a reboot works as a temporary solution. Removing the CRM temp files from "Diagnostics" doesn't help either.
Any ideas what might be causing this issue?