The value specified for the Low cut angle is not in the expected range. The vertical factor influences the total cost of moving into a cell by accounting for any vertical friction encountered. Determining the vertical cost for each cell is a two-step process. First, the prevailing vertical direction is defined by calculating the slope between each cell from the heights defined on the vertical-factor raster. This slope defines the vertical relative moving angle (VRMA). Once the VRMA is calculated, the vertical resistance to overcome the vertical factor is identified from the vertical factor graph. Since the VRMA is a degree of slope, it can only range from -90 (going down) to 90 (going up). The Low cut angle identifies the threshold VRMA at which any VRMA equal to or less than the angle is assigned to infinity for the VF. To function as a barrier, the Low cut angle needs to be between -90 and 0 since it defines the threshold to assign to infinity of a negative or downhill slope.
Make sure the specified Low cut angle is between -90 and 0.