I've got something very similar, but with an mp3 file instead of an m4a and the message is a bit different. This is weird because I've burned plenty of other mp3 files just fine (including ones downloaded from the same site), but now I'm having trouble.
I 23:30:49 ImgBurn Version 2.4.2.0 started!
I 23:30:49 Microsoft Windows XP Home Edition (5.1, Build 2600 : Service Pack 3)
I 23:30:49 Total Physical Memory: 2,095,088 KB - Available: 1,371,360 KB
I 23:30:50 Initialising SPTI...
I 23:30:50 Searching for SCSI / ATAPI devices...
I 23:30:50 Found 1 DVD