How to generate Digital Pulse using PXI-6238

Dear All

                  I want to produce Digital pulse from PXI-6238 or PXI-6704 or PXI-6527 ( i have all these)  with DAQmx 8.7.1 in LabVIEW 7.1. when i configure a channel in any of the above cards using DAQ assistant with continuse pulse/samples or N pulse it generates error 200077

Error - 200077 occured on DAQ Assistant

Possible Reasons:

Requested value is not a supported value for this property.
The property value may be invalid because it conflicts with another property.

Property: SampTimingType
Requested value: Sample Clock
You Can Select: On Demand

i like to generate pulse  up to  10kHz or even lower

Plz guide me.