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theres octalink for road and octalink for mtb
The difference between road and MTB is just axle length. The Sheldon Brown picture shows early & later Octalink, and applies to both road & MTB. The early version has short splines which proved too weak, so Shimano issued a second version with much longer splines and kept very quiet about the appalling balls up they had made of the first version.
theres octalink for road and octalink for mtb, dont know if that could be your problem....!
http://sheldonbrown.com/images/bbsx4-labeled.jpg