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After updating to High Sierra, did you install the drivers for the SZ? The drivers you previously had installed were functional for OS X Lion (10.7), but weren't even valid with 10.8 or higher. There was another driver set available for 10.8 through 10.10, but there is a newer set available for El Capitan (10.10) or newer. Please download and install that driver version for High Sierra, but also read the installation note on that page.