These are most likely bots looking for "hackable" programs and their default locations. If found, they would then attempt known hacks on the files.
cURL is a command line program to get, and more importantly submit, data as if you were doing so from a browser. It's positive use is to, say, submit a secure form on your site then send that data to a credit card processor then return the response to the browser so the user never leaves your site.
In this case they are using curl to try and "get" those pages, and there is a curl error. A quick Google of that specific error reveals very little; the curl error page [curl.haxx.se] doesn't list it so I can only **presume** this error is being generated by the rogue bot attempting to use curl and is an indicator your server settings are refusing all requests from cURL (?) Others may have actual accurate information . . .