I just saw that it really fails when debugging, as JP Alioto mentions ... and then if you go into the URL bar and exit again, IIRC loads at that moment. (It has been some time since I did this, so I could be wrong.) This is very strange. If you see this behavior when you are not debugging, it would be nice to get more details.
One point to note with WebBrowserTask is that it does not process URLs with &, I used Uri.EscapeDataString(url) before starting the task. This eludes much more than is required, but it does not have any negative consequences that I know of. (This could potentially mean that your maximum URL length will be significantly shorter than it would otherwise, I think.)
Jon skeet
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