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I'm attempting to install QGIS version 2.18.6 (64-bit). The installation gets close to completion, but before it finishes I get a message saying "Extract error writing to file..." I've tried installing several times, and a different file name comes up in the error message almost everytime (including qtgui4.dll, gdal200.dll, and others). Per another user's suggestion, I opened a command window and looked at the tasklist, but nothing comes up. I'm running as an admin and installing to the default program files (C:/Program Files). Any suggestions?