I'm using Lubuntu 15.10 and I have installed Chromium version 45.0.2454.101.
Use "make Chromium the default browser" not works (I not see any error).
The usual solution in Ubuntu is to open "Preferred Applications" - but I don't have that option on Lubuntu.
I have also tried update-alternatives.
There is only one alternative in link group x-www-browser (providing /usr/bin/x-www-browser): /usr/bin/chromium-browser Nothing to configure.
Any other ideas?
Updated with more info
Type asociations looks fine
$ xdg-mime query default text/html chromium-browser.desktop
Running $ chromium-browser on the console I see the following error each time that I click on "make Chromiun the default browser"
xdg-settings: unknown desktop environment