waveform contains values but MT downconvert generates an error

[Saila21]

Hello Everyone,

I am capturing data using a CompactRIO and a NI9775.  I am successfully capturing samples and have various measurements running on the complex waveform data type.

I am having issues with the Modulation Toolbox (which now appears to be a free download for LabVIEW) processing my data.  

I do not have an extensive background in DSP.

My issue is in demodulating an FM signal.  It is of low frequency both carrier and information, in the 10's of kHz carrier and hundreds of Hz information, and I'm sampling with the 9775 at 200kHz.  I can FFT and otherwise analyze the data using the Waveform toolbox (SINAD, etc) to confirm I'm gathering the data properly.  My measurements in labview of the captured signal match the signal generator settings and spectrum analyzer I'm using to monitor.

When I attempt to follow the MT FM demod example vi (simulated) methods, and replace the front half of that example VI code that generates the signal with my own real waveform signal into the Downconvert Passband (Real).vi there is the message:

error -21837

occurred at mod_Validate WFD Real Waveform.vi

Possible reasons:

Waveform contains no values

I have tried putting a probe on this line, and I can see that the waveform data is populated.  My power spectrum FFT wired to that waveform line even shows correct data before my vi halts on the error..

My configuration is the 9775 getting started (continuous mode) example of streaming data capture, with a couple of extra displays placed in the host VI. 

I have tried getting the components of the waveform, converting the timestamp so it is suitable, and then bundling that into the input of the FM demodulator VI as a test.  I get no complaints about having no waveform values then, however this doesn't demodulate properly (of course).

Does anyone know why this would be throwing an error despite there appearing to be values in the waveform?

Thanks for your help