Yaskawa MotionWorks IEC - Manual (Page 244)

PLCopenPlus Function Blocks for Motion Control 2013-04-13 236
override the "Stopping" state. Other blocks that try to cause
motion while MC_Stop has control of the axis will generate this
error. Also verify that the limit switches are not active by
checking the Global Variables for the axis. Also, a motion block
may be attempting to abort an MC_TorqueControl move.
4378 The function block is not applicable for the external axis
specified
57874 Argument data is NULL. The EngageData input must be
connected.
Example 1
Y_DirectControl configured for velocity mode.