After a few bad bugs were reported with 3.0.2, I had to remove it and go back to the coding board.
So, this new version finally corrects the problems with error -1762 (“Can’t get disk “OS X Mountain Lion Install Disk” or similar.). I performed about 20 different copies on different disks, each one was successful.
Download DiskMaker X 3.0.3 here (4,2 MB).
Oh, and BTW: DiskMaker X just went from donationware to RedCrossware. More info here.