Some cheap Biz class (and probably first class as well) fares do NOT allow a stopover. Generally if the further stop has a lower market price than the stopover point. One example of this used to be able to be seen on Expedia. For an example, Price YYZ-MXP (Milan) in biz class. Generally CP's price for the nonstop was about $1700 RT. KL would match that price IF there was not a stopover in AMS. Pull up "fare rules" and see. (Other fares in the $3k range for biz do allow the stopover).

Remember that a 23 hour stopover does -not- count against any free stopovers.

JL