Thank you for your post!
FileMaker 14 software started being much more picky about File Names and Paths that it would work with. Any non-alphanumeric character may cause an issue (aside of an underscore "_"). Rather than using hyphens "-" you might use the Underscore "_" or an Alpha-Numeric Character. This should allow the software to recognize the path/file name to open it.
I hope this helps and let me know if you have any further issue!
It doesn't really help because FileMaker is not dealing with the file names, these are in the batch file, so it's CMD that's screwing up the commands. (batch file exported to filewin:c:/temp/fmtemp.bat). The issue only occurs if the batch file is opened automatically as part of the export process. Opening the same batch file via any other method works correctly It would appear that there is something different in the way CMD is called in this situation.
(and changing the naming schema of digital archives containing hundreds of thousands of files is not a trivial workaround)
I have a functional workaround so it'll just be a case of running reports on all my databases to locate similar script steps and modifying them to open the file after exporting.