Nero 6.6.1.15a/b/c/d differences?

I downloaded all four of these 6.6.1.15 versions awhile back ago but I can’t tell which 6.6.1.15(x) is installed. What are the differences between these four versions?

Nothing I noticed except appearance and HD disc capability. I got tired of the bugs and decided not to buy. Moved back to 6.6.1.15d. It does everything I need quite nicely.

Sorry about the bad reply. I was thinking of another post I wanted reply to and selected your topic by mistake. :o

I don’t think there’s any major difference between those a, b, c, and d versions other than minor fixes, but I could be wrong. I’m using 6.6.1.15d since it’s the newest version of Nero 6 I could find.