You probably don't have permission to the camera. Try to use gphoto2 as root.
You you want to access the camera as a normal user (and you probably do), that user needs to have permission to proc/bus/usb/001/002 (depends on which usb-port you are using). Automatically giving users permission to the camera at connect is a little tricky.
Check this howto: http://digikam.free.fr/hotplug/howto.html