In Edit -> Preferences, under Audio -> Playback and Recording
Do you have 'Share Drivers With Other Programs' checked? If so, uncheck it, restart SONAR and try testing again. Your description sounds suspiciously like another application is opening the audio device at a different sample rate.
Short of that I'd reach out to support so they can get more information, driver mode setup etc and isolate the issue. We have just about every M-Audio device and tons of hardware synths we could test with as well if they had the lowdown on your configuration.