Redmine

Using Centos 5.5 I've installed two versions of ImageMagick (from sources), and then I install 'rmagick' 2.13.1 gem. With both of them I get errors when using the "export to PNG" feature in the Gantt view of Redmine 1.0.2:

- ImageMagick 6.4.9-0:
When I press "PNG" in Gantt view I get this error:

Processing GanttsController#show to png (for X.X.X.X at 2010-10-10 23:56:13) [GET]
  Parameters: {"format"=>"png", "month"=>"10", "action"=>"show", "year"=>"2010", "controller"=>"gantts", "months"=>"6", "zoom"=>"3"}

ArgumentError (unknown format: PNG):
  /usr/local/lib/ruby/gems/1.8/gems/rmagick-2.13.1/lib/RMagick.rb:1701:in `format='
  lib/redmine/helpers/gantt.rb:246:in `to_image'
  app/controllers/gantts_controller.rb:41
  app/controllers/gantts_controller.rb:39:in `show'

- ImageMagick 6.6.4-10:
When I press "PNG" in Gantt view I get this error:

Processing GanttsController#show to png (for X.X.X.X at 2010-10-11 00:05:45) [GET]
  Parameters: {"format"=>"png", "month"=>"10", "action"=>"show", "year"=>"2010", "controller"=>"gantts", "months"=>"6", "zoom"=>"3"}

Magick::ImageMagickError (Postscript delegate failed `/tmp/magick-XXzB9shs':  @ error/ps.c/ReadPSImage/779: `(null)'):
  lib/redmine/helpers/gantt.rb:245:in `draw'
  lib/redmine/helpers/gantt.rb:245:in `to_image'
  app/controllers/gantts_controller.rb:41
  app/controllers/gantts_controller.rb:39:in `show'

I've found some similar issues searching in Google, but all of them not clear without providing a resolution.