That is more than likely a power issue with the camera and/or CPU maxing out.
I was getting that after running it for awhile and noticed from this view that my FPS were bouncing all over the place, and even though BI was showing a consistent FPS, OpenALPR wasn't.
I switched the power supply to the camera and then FPS held constant and haven't had the problem since.
I think it also makes sense to follow the best practices of BI optimization for this camera - FPS and iframes match and since this can be CPU intensive, run the FPS as low as you can before it starts missing. I am running 8 FPS and catch everything. 15FPS would hit the CPU too hard.