[Tilecache] seed and "Did not get image data back" problem

[Oliver Christen]

Dear all

I have a problem with seeding a layer which use a restricted (and secured) 
wms serveur. That wms serveur limit the requests to a very specific bbox, 
all requests done with an extent outside of the restricted bbox are simply 
ignored by the server and the server return an empty anwer.

practicaly, when running tilecache seed script, I get some python exception 
with the message "Did not get image data back" and the seeding stop. (see 
full backtrace below)

I would like to know if there is a way to tell the seeding script to ignore 
such error and proceed to the next tile request ?

this is what I use to call the seeding script:
tilecache_seed CN25 0 5 502900,129500,504700,131800
(this is not the latest tilecache version, so it's the old syntax)

my layer definition in my tilecache.cfg

[CN25]
layers=pk25_komb10
type=WMSLayer
url=https://geoproxy.asitvd.ch/ogc/vd-wms-fonds
user=xxxx
password=yyyy
srs=EPSG:21781
bbox=501378,129183,506190,132220
resolutions=139.9999244000408, 99.99994600002917, 49.999973000014585, 
19.99998920000583, 14.999991900004375, 9.999994600002916, 7.499995950002187, 
4.999997300001458, 2.499998650000729, 1.999998920000583, 1.4999991900004372, 
0.9999994600002915, 0.49999973000014575, 0.19999989200005833, 
0.09999994600002916, 0.04999997300001458, 0.02499998650000729
mime_type=image/jpeg

the error traceback

Traceback (most recent call last):
  File "/usr/sbin/tilecache_seed", line 9, in ?
    TileCache.Client.main()
  File "/var/lib/python-support/python2.4/TileCache/Client.py", line 111, in 
main
    seed(svc, layer, map(int, sys.argv[2:4]), map(float, 
sys.argv[4].split(",")))
  File "/var/lib/python-support/python2.4/TileCache/Client.py", line 96, in 
seed
    svc.renderTile(tile)
  File "/var/lib/python-support/python2.4/TileCache/Service.py", line 138, 
in renderTile
    data = layer.render(tile)
  File "/var/lib/python-support/python2.4/TileCache/Layer.py", line 441, in 
render
    return self.renderTile(tile)
  File "/var/lib/python-support/python2.4/TileCache/Layers/WMS.py", line 29, 
in renderTile
    tile.data, response = wms.fetch()
  File "/var/lib/python-support/python2.4/TileCache/Client.py", line 64, in 
fetch
    raise Exception("Did not get image data back. \nURL: %s\nContent-Type 
Header: %s\nResponse: \n%s" % (self.url(), ctype, data))
Exception: Did not get image data back.
URL: 
https://geoproxy.asitvd.ch/ogc/vd-wms-fonds?layers=pk25_komb10&styles=&service=WMS&width=256&format=image%2Fjpeg&request=GetMap&height=256&srs=EPSG%3A21781&version=1.1.1&bbox=506497.997235%2C129183.0%2C511617.99447%2C134302.997235
Content-Type Header: text/plain; charset=ISO-8859-1
Response: