Ah, so you ran into one of discdump’s little bugs. If you re-boot and try again you may well find that you don’t get that particular message.
However, it doesn’t matter even if you do as the dump will still be successful if you allow it to continue (i.e. don’t hit the escape key to terminate the dump); it will just take longer (about 3 times longer with my reader).
What happens when discdump wrongly states that your reader doesn’t support fast sector skip and you allow it to continue is that it reverts back to standard mode which also works. (This isn’t surprising as discdump was originally programmed specifically for use as a safedisc dumping tool with what is now its standard mode being the only available mode.)
Btw, this is the correct forum for posts about discdump.
[PS You won’t have any problems using discdump to back-up GTAIII. That’s what I used when I made my back-up of that game.]
Using discdump through the burnatonce interface won’t prevent the “problem” raised by CCDKing from occurring. You just won’t know about it because burnatonce suppresses the dos box display of discdump’s command log when discdump is run through its interface. In the circumstances indicated by CCDKing all that would happen is that the dump would continue in standard mode without you being aware of the switch.