ERROR+Running AMS Design Prep

We run a demo mixed signal simulation on cadence AMS designer platform your_install_dir/tools/dfII/samples/tutorials/vfs_amsflow.t.Z
after a series of steps, I Run AMS Design Prep, the following Error appears in the message bar "Compiling vhdl.vhms in cellview VFS_AMS_PHY180.ADC.REF_LADDER_Behav./bin/sh:ncvhdl:command not found"
could you tell me how to solve this problem?
thanks!