[Tilecache] problem with mapnik layer

[Luca Delucchi]

Hi everybody, i'm so newbye about tilecache, i read something about it
and now i tried with a mapnik layer, my tilecache.cfg is this

[cache]
type=Disk
base=/var/www/osm_mapnik_tile

[osm-map]
type=MapnikLayer
mapfile=/home/luca/prova_mapnik_tile/mapnik/osm.xml
bbox=1016346,5510430,1029706,5522881
srs=EPSG:900913
#resolutions=0.01274108886718750000,0.00637054443359375000,0.00318527221679687500,0.00159263610839843750,0.00079631805419921875

but when i tried to see the png i have this error

http://localhost/cgi-bin/tilecache.cgi/1.0.0/osm-map/0/0/0.png

An error occurred: PSQL error:
FATAL:  Ident authentication failed for user "luca" in layer 'leisure'
  File "/var/lib/python-support/python2.5/TileCache/Service.py", line
287, in cgiHandler
    format, image = service.dispatchRequest( params, path_info,
req_method, host )
  File "/var/lib/python-support/python2.5/TileCache/Service.py", line
205, in dispatchRequest
    return self.renderTile(tile, params.has_key('FORCE'))
  File "/var/lib/python-support/python2.5/TileCache/Service.py", line
138, in renderTile
    data = layer.render(tile)
  File "/var/lib/python-support/python2.5/TileCache/Layer.py", line
411, in render
    return self.renderTile(tile)
  File "/var/lib/python-support/python2.5/TileCache/Layers/Mapnik.py",
line 38, in renderTile
    mapnik.load_map(m,self.mapfile)

My xml file is a good file because if i try it with mapnik i can print
a image, have you some advice for solve the problem?

thank's
Luca