card error message in .gpg-agent.log

[Seb]

Hi,

The following error messages are very common in my /tmp/.gpg-agent.log
(Debian sid system):

---<--------------------cut here---------------start------------------->---
2011-10-05 17:15:25 gpg-agent[2694] gpg-agent (GnuPG) 2.0.18 started
2011-10-05 17:21:36 gpg-agent[2694] error getting default authentication keyID of card: Card error
2011-10-05 17:22:10 gpg-agent[2694] error getting default authentication keyID of card: Not supported
---<--------------------cut here---------------end--------------------->---

What is causing these, and how to solve that?  Thanks.

Cheers,

-- 
Seb