You may not be able to use an installer to add NIRIO 3.2.1 to the LabVIEW 8.6.1 runtime engine from a previous installer.
Installing them together seems to work consistantly but using 2 installers fails if the first doesn't include NIRIO 3.2.1
This can be avoided if you always add the NIRIO driver to your installers.
The installer reports the following drivers are incompatible:
NI Measurement and Automation Explorer 4.6.1
NI-RIO 3.2.1
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