Hi Matthew,
I attempted to reproduce your issue last night and after a couple of hours of building and installing, I did not see the same behavior you describe. I built an installer in LV 8.5 on a development machine for DAQmx 8.6. On my deployment machine, I previously had DAQmx 8.5 installed and ran the installer I built on the development machine. I was able to successfully install DAQmx 8.6 on my deployment machine without any error message.
So at this point, I cannot reproduce your issue. One thing you might try is rebuilding the installer for DAQmx 8.6, if you haven't already done so. I would also try starting from scratch instead of simply rebuilding the installer you previously had for DAQmx 8.5; only include the installer for DAQmx 8.6.
Lastly, you might try reinstalling DAQmx 8.6 on your development machine and then rebuilding your distributed installer.
Let me know if this results in any new behavior.
Cheers,
Emilie K. | Applications Engineer | National Instruments