I want to set 1password shortcut for Firefox.
But, only the error "Alert" goes out.
I got the same problem, but I found a workaround.
It seems that 1Password does not work well with Japanese Input sources like Kotoeri and Kawasemi. The solution is setting the keyboard shortcut with an input source "U.S." (System Preferences - Language and Text - Input Sources). After setting your shortcut, you can disable the input source.
The same problem happens with other applications like Divvy.
I had the same problem but fixed it by the workaround. Thanks.