The LR 6.0.1 update is a small patcher for LR 6.0.0 so you need the LR 6.0.0 install done, first.
Hi Sprengel and Jon, thanks for the responses. SSprengel, I upgraded from 5.71 to 6.0.0 by downloading and running the Lightroom_6_LS11.dmg installer on April 21. Version 6 seems to be working fine except for the bug that sends me to a page-not-found when trying to access the online help.
99Jon, I've downloaded the patch from the direct download link that 99jon mentions and running it gives the error I described. Trying to update from the Help -> Updates menu tells me that "your applications are all up to date."
Last night after chatting with support I changed the permissions on both Library/ApplicationSupport/Adobe folders to allow Everyone to read/write. Still, the patch will not install.
I also created a new user and tried, unsuccessfully, to install the update from there.
Does anyone think I should uninstall and reinstall? And if so, what is the safe procedure to keep from losing work, presets, preferences, etc.? I think that if this is the recommendation, I'd wait for a more significant update, since essentially 6.0.0 is working for me.