Here a copy of the email sent to me from IB when I had the same problem:
This problem can be resolved by clearing the jar cache and repairing
explorer.
To do this, go to the control panel, click on the Java icon, go to the
cache tab
and click on the clear jar cache button. From there, go back to the
control
panel, go to add/remove programs in the control panel, down to
Microsoft
Internet Explorer, select add/remove and select the repair option.
-Ernie
IB Technical Assistance Center
I hope it helps.
Rene