You are using keyboxd in your new 2.4 installation which uses a sqlite database for the public keys instead of the old keyring format. You either have to switch off keyboxd or migrate your old keyring to the new format, see Gpg4win anouncement for 4.2 or for more detailed info the README of gpg 2.4.
As keyboxd is enabled by putting “use-keyboxd” in the file common.conf in your GPGHOME, you can disable it by commenting that line out in case you do not have imported any keys there yet. Otherwise you could use the gpg-disable-keyboxd script.
Keyboxd has the advantage of being faster than the classic keyring.
To migrate your old keyring to keyboxd see the instructions in the README of gpg2.4 or use the gpg-enable-keyboxd script shipped with gpg4win.