I hooked up a 9425 and then added a DAQmx property node(attached snippet) to your code, and set the sample clock source as ai/SampleClock. I didn't receive any errors relative to the clock, only an error about acquiring data since I don't have anything connected to the 9425. The Sample clock rate said that the sample clock was 140kHz, so I'm not able to reproduce the error you're receiving.
Andrew B.
Application Engineer
National Instruments.
http://www.ni.com/support
