Hey Randy-
That error can present itself when the version of the host driver software (NI-DAQmx) doesn't support the chassis you are attempting to Add. I'll assume you are using a version of NI-DAQmx 9.2.x (like 9.2.0 or 9.2.3). Is this correct?
The error has existed for a while for other networked devices, but, as you can tell, it is not particularly user-friendly. We added a more helpful error beginning in NI-DAQmx 9.3 to help avoid confusion for future users, but you were so ahead of the curve with your cDAQ-9188 that you are lucky enough to see that error now (pardon the sarcasm ).
The cDAQ-9181 chassis was first supported in NI-DAQmx 9.3, and the cDAQ-9191 chassis was first supported in NI-DAQmx 9.4. You can use that version or any newer version to support your chassis. This page is kept up-to-date with compatible device, driver, and firmware versions for cDAQ network chassis and NI-DAQmx.
If this is not your issue and you are in fact using a newer version of NI-DAQmx, please let me know so that I can try to offer more help.
Tom W
National Instruments