.net 3.5 IIS7.5 website can not be debugged - "Specified cast is not valid."

I'm trying to migrate an IIS6 site to 7.5, and in the IIS Manager's status section, I see "Unknown:Specified cast is not valid. (http). I've configured a base site that's just binding on port 80 to http. This doesn't stop the site from running. It does stop me from debugging though. When I hit F5 in VS, I get: "Unable to start debugging on the web server. Specified cast is not valid.". Digging into the EventViewer, I see a number of Informational messages that say:

Counter 0 of instance({some guid},[some number]_[AppPoolName], 0) could not be modified. Error: "The paramete开发者_如何学Gor is incorrect."

Other versions of the event list different Counter #'s. The user on all of these messages is IIS APPPOOL[AppPoolName] and the source is Diagnosis-PCW. Event ID: 16

That's the info I think is relevant. And now here's everything else that might be: I have VS 2010 Beta 2 installed.

Win 7 x64, the site has a number of custom modules and handlers we've written, one of which was our own MVC implementation (MS's was not ready at the time). I don't think this is the issue, because I at one point had a standard MVC site on there that was giving me the same error.

Thoughts?

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I'm not sure if this will help but here are two things to check/try out:

1. The application pool's managed pipeline is using the 'classic' mode.
2. 32-bit applications are enabled on the application pool. (if necessary)