Interesting error message on import

[Alphax]

On importing a large number of keys from a keyring backup, I saw the
message "gpg: assuming bad signature from key 0xE0BB4BCD due to an
unknown critical bit" about a dozen times. Can anyone explain what this
means, whether this is the correct behaviour, and if I should be worried
about it?

-- 
                Alphax
        Death to all fanatics!
  Down with categorical imperative!
OpenPGP key: http://tinyurl.com/lvq4g

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 569 bytes
Desc: OpenPGP digital signature
Url : /pipermail/attachments/20060622/4816b0ae/signature.pgp