Running out of CPU but System Levels only at 13-15%?

I am receiving an RTAS CPU overload error when mixing. I've got the buffers set to maximum. When I look at my resource usage, I don't see any spikes, and it seems to be staying around 14% give or take a little.



This does not always happen, and exiting the app and/or rebooting the machine seems to resolve it.



Any thoughts about why I am getting CPU overload if the usage meters don't reflect it?



Thanks.