My Keystation Pro 88 drivers dropping in X1D...

I've seen this about a half dozen times now. Session up  awhile - not using keyboard, but it's active in X1dPExp. Message pops up that the device is no longer connected, should Sonar re-route to an available device? Using the plug and play USB drivers. The MAudio drivers are crap for me. Anyone experience this, or know why that happens?
Thanks alot - Shep