SVT Gain & Phase - no gain value output

Our application has been using the SVT Gain & Phase.vi from the Sound and Vibration Toolkit
add-on for Labview with no problems until we try to upgrade.
The original versions in use are: Labview 8.2, Testand 3.5 and the Sound & Vibration Toolkit 4.0.
Basically, the SVT Gain & Phase.vi is used to return a gain value back into Teststand.
I ran our application using Labview 2009 and the
Sound & Vibration Toolkit 2009, a test based on the SVT Gain & Phase.vi failed.
Stepping through the code showed that the VI was not returning a dB gain value, but "Nan" instead.
Also the function would generate an error, details are:
Error code: -1945
Basic detail: The fundemental tone was not detected.
I also tried our application with Labview 8.6 and
Sound & Vibration Toolkit 7.0, this also produced the same problem.
When I looked closely at the other output values of the VI, detected frequency
and amplitude of the signals, these values were comparable with all previous passed
tests, despite the error with the gain value.
In fact, because the detected amplitudes of the signals were correct,
I was able to manually calculate the gain value even though the VI couldn't.
On one hand the function is correct to complain about one of the input signals
because it's not perfect, but why should the VI from an earlier version of
the SVT not generate an error ? Is the newer VI version less tolerant ?
Thanks,
Gary.

Dominic,
Thank you for your reply.
With reference to your question about the phase, it's something I cannot answer at this
moment as the phase value is not something we monitor.
Looking closely at how we are using the SVT Gain & Phase.vi, I realised there is scope
to improve the response signal y [EUy] value that is passed in.
By increasing the number of samples obtained from the output of the unit under test by
10 x, this gives a waveform with which the VI is happy to "detect the fundamental tone".
And so the gain value is returned as a number and not "Nan".
For the time being it's the solution we are happy with.
regards,
Gary.

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