Seems as though Capital One may have run into some issues with the mobile banking section of their website. Windows Phone Junky reports that it was recently updated, but while improving the user experience the team behind the development seem to have broken compatibility with Windows Phone 7 devices when attempting to browse an account.

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On a quick side note, found it interesting to see their main homepage throwing a compatibility warning with Firefox 4:

Are you with Capital One and use their online banking? Do you experience this problem with their mobile site on your device?

Source: Windows Phone Junky