I should not really post here as it not specifically a Sonar issue but I am hoping more people will see and chip in.
I have been having problems with my Cakewalk A-PRO 800 keyboard controler outputting spurious MIDI messages. See here for the full story http://forum.cakewalk.com/FindPost/3351294
 
I changed the A-PRO driver setting to Light Load and the problem seems to have gone away. Light Load apparently reduces the polling frequency, is it logical that would stop the spurious messages??
 

Not "logical" but consider the scenario where electrical noise in the system is producing very brief transients. A faster polling frequency would catch more spurious events, than a slow one which might be reading only longer event durations, or simply missing the events between readings. Are you certain that the only thing that happens with "light load" is a change in the frequency of polling? It would be reasonable that the sensitivity might be increased as well. 

slartabartfast
Not "logical" but consider the scenario where electrical noise in the system is producing very brief transients. A faster polling frequency would catch more spurious events, than a slow one which might be reading only longer event durations, or simply missing the events between readings. Are you certain that the only thing that happens with "light load" is a change in the frequency of polling? It would be reasonable that the sensitivity might be increased as well. 

Thanks, that makes sense. The help is not that helpful when it comes to Light Load, it just says you do not normally need to use it. The discription I found actually applies to a Roland UA20 so it may not be totally accurate. I am keeping my fingers crossed but I have been noodling for several hours today and recording it and have not caught one case of spurious data.