set the rate of sample clock

Hi, 

I am continiously reading a digital signal with a simulator. I would like to know how can I check at what frequency the signals are coming back?

How can I set internal clk?

When I use 'ConfigureSampleClock' to setup the external clock, I get error: Requested value is not a supported value for this property. The peroperty value may be invalid because it conflicts with another property. 

Status Code: -200077 

I am getting the same error with ContReadDigChan_ExtClk sample. 

I will use NI USB-6002 for the actual project. 

Thanks,

Shabnam