There is a hard coded limit on the number of times a tune purchased through iTunes can be copied (burned to CD/DVD). If memory serves the limit is 8.
The limit (which my memory says is 5) is not a per-track limit. It's a per playlist limit.
That is, make a list of 8 tracks. Burn it 5 times. Delete a track from the list, and add a different one. Burn 5 more times. Change the order of the tracks in the list. Burn 5 more times. Repeat as often as desired, so long as not more than 5 discs have the same tracks in the same order. There is of course no limit if all the tracks are DRM-free.
A workaround is to burn the track(s) once to CD, then re-import from the CD. The re-imported tracks will be DRM-free, and can be burned as many times in whatever order as desired. There may be some tiny loss of fidelity from the AAC to AIFF to AAC (or MP3) conversion. Or, burn one CD just the way you want it, and then duplicate that CD forever. Either way, you're exploiting what is known as the "digital loophole".