SparkViewEngine spontaneous NullReferenceException while rendering view

We are using the latest stable release of SparkViewEngine for www.stribe.nl. There is a problem that occurs -sometimes- while rendering the homepage. When you look at the homepage it will usually render perfectly fine, but i noticed some exceptions in the EventLog from people visiting the homepage.

The exception message is "Error executing child request for handler 'System.Web.Mvc.HttpHandlerUtil+ServerExecuteHttpHandlerAsyncWrapper'" which means an exception occured while executing a ChildAction on the controller.

So i ran the site in VS2010 debug mode and started a stresstest tool that requests the homepage a few times per 10 seconds. After running it for a few cycles of 10 seconds it breaks in开发者_如何学JAVAto my code (see screenshot).

Output (which is the sparkview output buffer) is null. When i continue running the code after the exception it will give the exception about child request failing and then it renders the rest fine (and next request the whole page just renders without problems again)

This happens over and over again, but the times on which it happens seem random, same as the location in code where it happens seems random. I have no idea what is going wrong here (it's one of those "it happens sometimes" bugs) and also no way of analysing it further than i did now.

Is there anyone with SparkView experience that maybe got this problem too or has any clue on to what may be the problem? Or anyone with ideas on how i can analyse this issue better?

alt text http://www.stribe.nl/sparkerror_null.png