Solved! Go to Solution.
You can try to install the currenct EV client on Outlook 2010 and see what happens.
In this thread: https://www-secure.symantec.com/connect/forums/ev-support-outlook-2010 someone has installed the EV 7.5 client in Outlook 2010 and seems to be able to open archieved files. Just give it a try, but note that this configuration will not be supported by Symantec.