Originally Posted by
tommyd49
Spacer between the 6th and 7th sprocket?
+1
At least that's the way my new 7 speed cassette came.
What are you changing from, and to what?
IF the new cassette has an 11T cog, and the old one didn't you'll (most likely) have a problem. An 11T cog requires a "Compact" Freehub.
http://sheldonbrown.com/k7.html#11