the slowing down means the CD wasn't burned very well, the drive has to slow down when reading to be able to read the data correctly.
try burning the media at a lower speed, see if that helps.
as for the long filenames, yes that can be a problem.
(i'm not saying it is in your case, but it might).
try shortening the name.
assuming you're using Nero 5.5, in the compilation window the files whose names are too long will be shown in italics, so you should be able to see if some files have names that are too long.
also, before the burn actually starts, Nero should warn you that some files have long names (unless this feature was "turned off". to be sure this feature is "on", click in the menu-bar File -> Preferences, in the General tab the 4th checkbox is "Check Joliet filenames before burning", make sure it is checked).
to check which versin of Nero you have, click in the Menu-bar Help -> About Nero.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor, where the Shadows lie
M.C. Escher - Reptilien