It looks like all of the affected sites have issues related with 'Adsense' and 'FeedExplorer'.
Any advice from a DNN core team member about the best way to fix this?
Thanks,
Horacio.-

the correct thing at this point would be to log this as an issue at support.dotnetnuke.com so it can fixed in 6.0.2 - ideally provide a copy of the database as well as the site

However if you wish to try to manually fix it - you could try the following
Note:if you're not using the adsense module, try uninstalling it - same with feedexplorer. However if you are using either then:

Presumably this error is caused by some previous update that failed to remove/update values correctly (or else a 3rd party module that used the same naming and caused an issue). Take a look at the value in the controlsrc for the duplicate entries and then check to see if that file exists in your website - if it does not then you can remove it (as if that key is requested it will fail to load the files).
After removing the duplicates, ensure that you clear the cache - tools->recycle application pool from the top menu should do this - now check and see if that resolves.

Note:controls can have the same controlkey if they are keyed to different modules e.g. most modules have edit and settings controlkeys but as long as theres only 1 per each moduledefid thats fine -controls can also have no moduledefid i.e. admin/host controls - take extreme care before touching those controls.

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I am not using either Adsense or Feedexplorer. If I uninstall them, is it possible to then upgrade w/o issue?