Have a D-Link IP camera that just stopped working for no apparent reason and now you're getting an HTTP 400 message from it?
I've been fighting with this for quite some time, some of my systems work, some don't, some just seem to stop, resetting IE7 doesn't fix it.
The culprit is Silverlight. Removing it, restores the cameras functionality.
If you have access to connect.microsoft.com, please go there and add your feedback that you can validate this and rate it's importance. Silverlight feedback is under Visual Studio, the existing bug ID is 340906.