the plugin creates the SVG file by itself from your GPX track, so you don't have to create it yourself. It then tries to store the SVG file in the folder where your GPX file is located.
This can fail if the user account has no write access in that folder, so that would be the first thing to check.
If you don't need the elevation diagram, then simply turn it off in the plugin's configuration (Elevation diagram tab -> set "Show elevation diagram" to "no"). With that setting, the plugin will not try to create the SVG file and write it to disk in the first place.