Then check out this new KB article (KB2512239)

Netflix in Windows 7 Media Center may encounter an error when it initiating video playback after you install Internet Explorer 9 RC

After you install Windows Internet Explorer 9 Release Candidate (RC) on a computer that is running Windows 7, the Netflix application in Windows Media Center may encounter an error when it initiates video playback

There is the usual Microsoft Fix it as well (50624)

Fix problme with Netflix, WMC and IE9RC

thanks to DanMa for the tip

Rob