6509 is running IOS ver 72033.advipservcesk9_wan_mz.122-33.SXH2a
3750 stack consists of one 3750g-24ts and one 3750-24p running ipbasek9-122.46(SE).
When each end configured for "channel-group n mode on" the 3750 ports go into err-disable. With each end configured for "channel-group n mode desirable" 3750 will fail because PAgP does not work across stack, etherchannel ports need to be on same switch.
Has anyone else seen this problem and what action was taken to overcome this problem?
Follow this link to setup the Ether-Channels
Hope This helps