Can fast cavalry shoot when they march? If so what penalty to WE glade riders get.
Son of Horus, I will have to contradict you.
Looking at the boxed section of page 18 of the Wood Elf army book, it mentions "Wood Elf longbows" as not suffering the move and shoot penalty.
Since Glade Riders are armed with longbows this rule applies to them and they are also fast cavalry which leads us to the conclusion that they can indeed march and shoot without penalty.
I'll have a look at the FAQ to see if this has been overruled.