Bug#459344: closed by Otavio Salvador <otavio@debian.org> (Bug#459344: fixed in apt 0.7.13)

[Torbj|rn Andersson <d91tan@Update.UU.SE>]

In my case it seems I get the error mail, not because the cache was 
locked by another process, but instead because I have a few unmet 
dependencies on my system.

This is, of course, entirely my own fault. It would be nice if the 
error message could be a bit more informative, though.

Torbjö  nAndersson