a quick fix would be to add a number or letter after the filename in the parameters 1 tab. the part that shows the whole directory...
http://img77.imageshack.us/img77/9601/picture1fl2.png
works for me when this happens...
though recently our raids have been mysteriously dividing... only shake and color recognise it as fragmented drives... weird, but if I render to the wrong one it just vanishes?!