Concurrent programming

Hi guys (Brad :)), I have been trying to generate a filtered image on a different thread using the iOS 6 way (NSOperationQueue), I am getting always at some point the error: "Error at CVOpenGLESTextureCacheCreateTextureFromImage -6683".
Is this because GPUImage has already its own thread management (see runSynchronouslyOnVideoProcessingQueue)?

Is there a way to apply filters to images on a different thread?

Thanks!