Description
The specified keyword for horizontal factor type is invalid. Vertical factor parameters define the relationship between the vertical cost factor and the vertical relative moving angle (VRMA). The parameters are composed of a keyword specifying an existing graph or table for a custom graph created from an ASCII file and modifiers. The keyword parameter and modifiers need to be in quotes. Spaces must separate the keyword and modifiers. The format for vertical parameter modifiers is "modifier_name=value". Valid vertical keywords are BINARY, LINEAR, SYM_LINEAR, SYM_INVERSE_LINEAR, COS, SEC, COS-SEC, SEC-COS, and TABLE.
Solution
Make sure a valid keyword is specified for the vertical factor. The documentation for how Path Distance works gives more information on the formatting of the parameter file.