01. Posting a request, and then again and again - all within nine (9) minutes ...
02. Information not provided: Macintosh model, MacOS X version, 'iTunes' version, manufacturer and type of disc burner [1], manufacturer and type of media, was Mac (very) recently updated? - if so, what was / were the updates(2); and, from what version(s)?
03. A Google search reveals these
results.
The general consensus: Relaunch 'Finder' [2], try new media, attempt to clean the disc burners' lens, and / or replace the disc burner.
[1] - Launch 'System Profiler' (in the '/Applications/Utilities/' folder), click on 'Hardware's' disclosure triangle (to point it down), click on 'ATA', and finally note the burner listed in the upper right panel list, under the (or one of the) 'ATA Bus' heading(s). Clicking on the burners' name will reveal additional information - in the lower right panel.
[2] - Press and keep pressed the '<option>' key as you click on 'Finder' on the 'Dock', and select 'Relaunch' from the resultant menu that appears.