How to debug tirex with mapnik backend

I have installed tirex and the mapnik backend.

The test tiles from tirex are working fine, but if I use a real mapnik map, and access the tile server I am getting a 404 error after some seconds.

How can I debug this issue?

I am getting only a fee lines of log output:

==> /var/log/syslog <==

==> /var/log/tirex/jobs.log <==

==> /var/log/apache2/error.log <==

==> /var/log/apache2/other_vhosts_access.log <==

==> /var/log/apache2/error.log <==
[Sun Nov 04 19:54:23 2012] [info] [client 10.0.2.2] tile_storage_hook: handler(tile_serve), uri(/osm/1/1/1.png), filename(/var/lib/mod_tile/example/1/0/0/0/0/0.meta), path_info((null))
[Sun Nov 04 19:54:23 2012] [info] [client 10.0.2.2] Requesting style(example) z(1) x(1) y(1) from renderer with priority 5

==> /var/log/apache2/other_vhosts_access.log <==
tile.mytileserver.org:80 10.0.2.2 - - [04/Nov/2012:19:54:23 +0000] "GET /osm/1/1/1.png HTTP/1.1" 404 502 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:16.0) Gecko/20100101 Firefox/16.0"