The horizontal factor influences the total cost of moving into a cell by accounting for any horizontal friction encountered. Determining the horizontal cost for each cell is a two-step process. First, the prevailing horizontal direction is defined by a horizontal-factor raster. The values range from 0 to 360. Once the prevailing horizontal direction is defined, the horizontal relative moving angle (HRMA) is calculated. The HRMA is the angle difference of the direction of moving into a neighboring cell and the prevailing moving direction defined by the horizontal-factor raster for the processing cell. The HRMA can range from -180 to 180. It is assumed that the horizontal correction angle is symmetrical on the horizontal-factor axis in the horizontal-factor graph; therefore, the HRMA should be between 0 and 180 degrees, inclusive.
Review and correct your horizontal parameter file if there is an angle less than 0 degrees.