It seems that Mackie ASIO driver is not seen by JUCE - two of our users (of TruePianos) reported that. Other applications can see and use the driver.
I located the potential source of the problem, and it seems to be the checking for existence of InprocServer32-valued file name in the ASIO enumerator (checkClassIsOk function).
The older version of JUCE (which had non-functional checking via OpenFile) worked fine, could see and use the driver, as it seems. So I wonder - it looks like the file can be missing, however the object/driver being loaded fine. It could be about WOW64 filesystem virtualisation. I could not reproduce this on my own machine or get the exact information from our users yet, but I believe this might be possible, if the file is placed inside System32.