Problem: Operation Failed [using Shortest Path function]
The Shortest Path function in Spatial Analyst, when using the output distance and direction rasters generated by the Straight Line Distance function, returns the message:
The Shortest Path function is designed to work using the output distance and direction rasters generated by the Cost Weighted Distance function, not by the Straight Line Distance function.
Solution or Workaround
Generate distance and direction rasters with the Cost Weighted distance function. Use these as the inputs for the Shortest Path function.