My own experience burning CDs (which dates back to when Windows 95 was first released) is that discs burned at higher speeds are not as easy to read as discs burned at lower speeds. This holds true whether I am burning an audio CD for my old Ford truck that rides very rough (faster burn speeds=skipping audio) or an auto installer for one of my modded Xboxes (faster burn speeds usually do not boot). I have also found that discs burned at lower speeds are easier for drives to read that were never intended to read burned discs to begin with (ie early PS2s).
Maybe you're burning too slow, try to burn it at 16x. Burning too slow is like lying in the sun for to long, you'll get burned, and so does the disc when it's exposed to the laser too long.
Keep in mind that all a CD burner is doing is changing the color of dye on the disc. The slower the disc spins by during the burning process, the longer the laser has to do a complete and darker "burn". I have had countless occasions over the years where brands of cheaper media would produce nothing but coasters when burned at their rated speeds but will produce perfectly readable discs when burned at lower speeds.
I realize that a lot of folks never need to adjust their writers burn speeds, but remember that we are doing things that Sony never made allowances for, so sometimes we have to modify what would be a standard procedure to get these non-standard results.
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