Vassal would not read vdmx files

[otto]

Hi there,
I right click on the on the PG - huber module,
choose add extension,
select - as reccomended - the core data minefields file
...get and errore message stating: Vassal was unable to write the file ...Core_Data--Panzer_Grenadier_Uber_base_module_ext
Could anyone be able to help me with it?

I'm using Vassal 3.4.7 ...too advanced?

Thanks a lot
Ottavio