Forum Member itzbinnice could be correct in his assessment concerning your DVD Burner in seeing that you recently had repair work performed on you Lap Top.
There are a couple of things you could check before returning your Lap Top back to the repair shop for your DVD Burner problems.
The problem you are reporting could possibly be caused by DVD media incompatibility between your DVD Burner and the particular DVD media you are using. If you are experiencing difficulty with your DVD media it is prudent to insure that your DVD Burner has the most current up to date firmware available for your DVD Burner installed.
To determine the current firmware of your DVD burner use a software utility similar to DVDInfo Pro (http://www.dvdinfopro.com/). Toshiba released firmware version 1M34 for the Toshiba SD-R6012. If your firmware isnâ€™t this version suggest installing the newer firmware.
Suggest visiting The Firmware Page for Toshiba DVD Burners (http://forum.rpc1.org/dl_firmware.php?category=14&manufactor=31) for obtaining the latest firmware available for your Toshiba SD-R6012 DVD Burner.
Your problem also could possibly be DVD media related. If you have the most current up to date firmware available for your DVD Burner and your problem still exists you need to ensure that you are using known good reliable DVD media.
Suggest visiting the CD Freaks Media Forum (http://club.cdfreaks.com/forumdisplay.php?f=33) and see which DVD Media other Forum members have reported as good reliable DVD media.
Also suggest slowing down your burning speed. Limit all background activity while Burning DVDs including Ant-Virus programs. Defragment your Hard Drive (Start/Programs/Accessories/System Tools/Disk Defragmenter). Check for Spyware by running Spybot-Search & Destroy (http://www.spybot.info/en/index.html)
The above suggestions are just a shot in the dark but before returning your Lap Top back to the repair facility itâ€™s worth a try.