I have solved this problem on my computer (Chrome 64bit and Win 8.1 64bit) this way: 0) Close Chrome (i do not think it is really necessary) 1) start -> regedit -> enter On the left tab: 2) HKEY_LOCAL_MACHINE->SOFTWARE -> Classes 3) Right click on Classes, new key, name the key 'nxm' On the right tab: 4) Double click on (Default) (I'm not sure, in italian it is called (Predefinito)) and paste 'URL:nexus mod', click OK 5) Below, right click, new string, name the string 'URL Protocol' On the left tab: 6) Right click on nxm, new key, name the key 'shell' 7) Right click on shell, new key, name the key 'open' 8) Right click on open, new key, name the key 'command'On the right tab: 9) Double click on (Default) (I'm not sure, in italian it is called (Predefinito)) and paste '"(Path to mod organizer)\ModOrganizer.exe" "%1"', click OKthen close the regedit. NOTE: when you copy-paste the values, copy only the letters inside the ' but not the ' itselfs. Sorry for my awful english.