Hello,
I have not seen this issue before, but I would suggest the following troubleshooting steps if this is definately an issue for only one user.
1: Log onto another PC/Laptop ensuring the user does not have a cached profile nor is using roaming profiles. Does this work correctly now? If it does rename old profile under Documents and Settings and recreate on own PC/Laptop.
2: Re-Install EV Client extensions.
3: ZAP the users mailbox. For more info on this go to support website and search for ZAP which should take you to the technote concerned.
4: Ensure EV server has been applied to IE in local Intranet Zone both in FQDn and Netbois name format.