That rings a bell! If you're using a an old version of ArtRage 2.0, grab the latest updated installer from www.artrage.com/artrageinstaller.html and install this.
We found the following bug in 2.05 and fixed it with 2.2 and later versions
'Fixed a bug that was causing checkers to be exported to the background of transparent PNGs. '
If you're running the latest version ( 2.5.20 ) let me know, as well as the operating system you're using, and I'll check it out with you. Hope that's of some help!