Since end of november kgpg was throwing errors popup when starting, root cause being gpg issues :

gpg: Oops: keyid_from_fingerprint: no pubkey
tru::1:1416945128:1423745807:3:1:5
rvk:::17::::::3FC732041D23E9EA66DDB5009C9DBC21DF74DC61:80:
rvk:::17::::::19D03A15999E5DFEC360071E9420CF3BC2C08F9E:80:
rvk:::17::::::52064C78B5D875779B3691A2A891DD4308010A5F:80:
rvk:::17::::::23955BF5A6F0DC753B637DD11331DB747AFF2E92:80:

After longer google search I came across a post on the GnuPG mailing list that gave me the hint that GnuPG v2.1 has dropped support for older v3 keys by removing support for MD5 hashes.

And in fact, Arch Linux introduced GnuPG v2.1 around the end of november timeframe.

There is no easy workaround for this like setting a flag in a configuration file - MD5 hashes are past.

Using an older version of GnuPG on a Ubuntu Saucy box, I could get ascii dumps for each public and private key in my keyrings. Then I imported them into freshly created keyrings.

Turned out that the eldest of my four private keys and 10% of my public keys were using the old format and thus could not be imported.

According to this site it is possible to convert old keys to the new format, but there was no need to do so for me.