Error -50 whilst burning with Toast titanium 10.0.6

Hi, I burnt one video dvd no problems, set my imac to burn a different set of video to dvd and it starts doing theltiplexing, soon as it needs to burn, I get pop up message ..Could not burn the disc because of a Mac os error.. result -50..
I have checked for a firmware update but couldnt find one.. my imac has the Optiarc ad-5680h version 3AHB.
Anyone know what's up? this Imac is only 1 and half months old. Dvd drive used twice.....