When Outlook is opened, an error occurs stating that the Symantec Addin is no longer available.
This error is a bug in the Symantec removal process - it doesn't remove this particular reference from Outlook when it is uninstalled!
In Outlook, go to Tools/Trust Center/Add-Ins.
Near the bottom, there is a pull-down menu. Change the selection to: "Exchange Client Extensions" and click "Go:".
Uncheck "Symantec Antivirus 10.1" and click "OK".
Close & reopen OUtlook and the message should no longer appear.