You are making a custom framebuffer driver?
ls /dev/fb* lists fb0, so the file is there.
Yes, but you actually have to issue the command and copy/paste it and the result here so we can see what you do. That way your report looks like this:
$ lsmod | grep fb
fbcon 36640 72
tileblit 2460 1 fbcon
font 8124 1 fbcon
bitblit 5372 1 fbcon
$ ls /proc/devices
$ ls -l /dev/fb*
crw-rw---- 1 root video 29, 0 2010-02-08 01:20 /dev/fb0
$ cat /dev/fb0 > myfile
(In my case it worked).
See how I have put the command as well as the result? This way it is unambiguous what I have done and others can be confident they have all the facts. (Note the -l option in the ls command? That is important because your error says "no such device" not "no such file" - perhaps it is the wrong kind of file?)