First, verify that your player will read AVCHD (if possible).
If you are confident that it can, then one of the following is probably at fault:
1) Your download is bad. You can check the MD5 hash, or download again.
2) Your burner is bad.
3) Your DVD is bad.
4) The combination of your burner/DVD isn't producing a quality burn.
5) You took a wrong step in the Disk Utility.
Out of the 5, #5 is the most common and #4 is the next most common. I don't have a Mac, so I can't...