Sorry to hear you had a problem. If the file is 0 bytes in size, then unfortunately it won't be recoverable. If you're on Windows, check that the 0 byte file is the one you saved, rather than ArtRage's arrestart.ptg file which is the one ArtRage attempts to automatically save when there's a crash. If it's your file, check the following location for arrestart.ptg
run 'Application Data'
open Ambent Design\ArtRage 2\ <- the file is here if it was saved
Windows Vista / 7
open Roaming\Ambient Design\ArtRage 2\ <- the file is here if it was saved
See if that file exists and can be opened. If it can, save a copy as a different filename in your normal location and continue working from that, rather than the arrestart file. If it can't be opened but has data in it, you can email the file to me at email@example.com and we can take a look at it here for you to see if anything can be recovered. If it's larger than 10mb let me know and I'll sort out another way of getting hold of it.
I tend to use multiple files when I'm working on time consuming or large files in general e.g. mypainting1.ptg mypainting2.ptg and saving fairly regularly, as this means I'll at least have an older version of the file in the event of file corruption, crash, power failure and so on.
I hope that's of some help!