Corridor planning in HBM - warning regarding illegal characters in output filename

Hi, I'm getting a warning message when trying to use the HBM planning module for corridor planning that my output filename may include illegal characters or that the output already exists. I am using the tutorial data downloaded from the Terrset website with no modifications and naming conventions exactly as specified in the tutorial. There are no existing files with filenames "CORRIDOR3_5" (recommended as the output file name for thie operation in the tutorial) in my working or resource folders. My inputs are 2 terminal regions (generated and named exactly as specified in the tutorial), and the habitat suitability map (HabitatSuitability99CMA) provided with the tutorial data, Any recommendations? Many thanks, Craig