Solution
This warning can be seen with a generation VST, and a similar one can be seen with the acquiring side of the VST. It can be seen in the RFmx Soft Front Panel, the NI-RFSA Soft Front Panel, the NI-RFSG Soft Front Panel, and the LabVIEW IDE.
To make the warning go away, the easiest method is to perform a self-calibration. Follow the steps explained in the following link to do so,
Self-Calibrating a VST Device. If the Self-Calibration fails with error -1074097149, check the
Error -1074097149 When Self-Calibrating a VST article.
If your instrument has been calibrated within the recommended interval (usually 1 year), the data's accuracy should be ok. However, the best is that once the warning has been cleared, the instrument is compared to a known standard.