I have the same problem as well, but have discovered that the problem doesn't exist for me in Firefox. That's quite the shame, as I rather prefer IE. I couldn't make it work with IE6, so I downloaded and installed IE7 and still got the same error. That's also quite a shame, because IE6 seems to work better with Outlook Web Access better than IE7 does. Some IE architect in Redmond seriously needs to find a new position elsewhere.
OLW people -- this is a neat product, and it is part of a whole string of really neat things MS has been rolling out of late. You really, really need to get IE to talk with it better -- fill their RAID with bugs if you have to, just get them to start testing this seriously. Using Firefox as a workaround is crap.