Arria 10 GX DevKit Windows Installer?

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Hmm. You mention you have 15.1, not 15.1.2 installed. Have you tried updating Quartus?

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Tried both 15.1.0.185 and 15.1.2.193. No difference. Thanks though.

UPDATE:

Tech support suggested updating java and editing environment variables.

That seems to have done the trick and it now works on two of the three PC's with Quartus Prime 16.1. Still getting a missing DLL error on the third PC, which is unrelated.

Thanks for helping.