Can't update from 2017r2.1 to 2018r1.1

Was able to update from 2017 r1.1 to 2017 r.2.1. Error: An error has occurred while downloading. The download could not be started because the temporary file could not be written to. Mac Sierra; 2010 MacPro. Thoughts?

There usually is a time check. Restart the web page and click back in the original link to download the file.

This was a problem with trying to update from within the IDE. Problem (as almost always) was a hardware error between the keyboard and the chair, but I post here in case any one else has the issue: I had downloaded the upgrade some number of months ago, but forgotten. For an unknown reason, launching XOJO was launching the earlier version. Attempting to upgrade was failing because the upgrade was already in place–but the error message was cryptic enough it didn’t trigger the recollection.