Requests stuck in RequestAcquireState in IIS worker process

On 开发者_StackOverflow社区one of our production servers, occasionally requests get stuck in the RequestAquireState while in the session module. As it is an MVC request, it does not timeout, so we sometimes get requests that run in the background for several hours.

We are using the standard asp.net session module on .net4 and IIS 7.5 We are using InProc.

Why would it get stuck?

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Had the same problem when running with Asp.net State Server, restarting the service resolved the problem.