Hello.   I'm writing v9 chook now and trying to add drive surface to new operation. all surfaces are selected with SELECT_BIT. but when I called code below, selected surfaces are added as check surface...not drive surf...   any idea?   Thank you code: surface_manager ( op.op_idn, // I: operation id to edit &chains, // IO: ptr to list of chains if using SRFMGR_CHN_*** SRFMGR_SRF_ADD, // I: what you want to do 1, // I: 0=drive