Are you using a European Laptop? With a non UK language?
When using this version of Cosworth Map Generator Tool from a European Laptop, it is important to ensure that the PC Numbering system is in UK format (i.e. one thousand = 1,000 not 1.000)
To do this, go to Control Panel, "Clock Language and Region",
Then click on "Change the date, time, or number format",
In formats, make sure the format is set to "English (United Kingdom)"
You should now be able to generate the .gpx file.
Once this is complete you can then restore the numbering system back to the original.
We are looking to rectify this issue in future releases of the software, however this is the fix for now,