As far as I remember I have not make much change in the config file. May be it is the video card driver that makes a difference. If the off screen buffer is created as parasite-buffer, it won’t work.
###########################################################
### ###
### Panda3D Configuration File - User-Editable Portion ###
### ###
###########################################################
# Uncomment one of the following lines to choose whether you should
# run using OpenGL or DirectX rendering.
load-display pandagl
#load-display pandadx9
# These control the placement and size of the default rendering window.
win-origin 50 50
win-size 800 600
# Uncomment this line if you want to run Panda fullscreen instead of
# in a window.
fullscreen #f
#sync-video 0
# The framebuffer-hardware flag forces it to use an accelerated driver.
# The framebuffer-software flag forces it to use a software renderer.
# If you don't set either, it will use whatever's available.
framebuffer-hardware #t
framebuffer-software #f
# These set the minimum requirements for the framebuffer.
depth-bits 16
color-bits 16
alpha-bits 0
stencil-bits 0
multisamples 0
# These control the amount of output Panda gives for some various
# categories. The severity levels, in order, are "spam", "debug",
# "info", "warning", and "fatal"; the default is "info". Uncomment
# one (or define a new one for the particular category you wish to
# change) to control this output.
notify-level warning
default-directnotify-level warning
# These specify where model files may be loaded from. You probably
# want to set this to a sensible path for yourself. $THIS_PRC_DIR is
# a special variable that indicates the same directory as this
# particular Config.prc file.
model-path $MAIN_DIR
model-path $THIS_PRC_DIR/..
model-path $THIS_PRC_DIR/../models
sound-path $MAIN_DIR
sound-path $THIS_PRC_DIR/..
sound-path $THIS_PRC_DIR/../models
texture-path $MAIN_DIR
texture-path $THIS_PRC_DIR/..
texture-path $THIS_PRC_DIR/../models
# This enable the automatic creation of a TK window when running
# Direct.
want-directtools #f
want-tk #f
# Enable/disable performance profiling tool and frame-rate meter
want-pstats #f
show-frame-rate-meter #t
# Enable audio using the OpenAL audio library by default:
audio-library-name p3openal_audio
# Enable the use of the new movietexture class.
use-movietexture #t
# The new version of panda supports hardware vertex animation, but it's not quite ready
hardware-animated-vertices 0
# Enable the model-cache, but only for models, not textures.
model-cache-dir $THIS_PRC_DIR/../modelcache
model-cache-textures #f
# Limit the use of advanced shader profiles.
# Currently, advanced profiles are not reliable under Cg.
basic-shaders-only #t
#sync-video 0