Got it few days ago from this page.
So there's one Gp5 file which I can only run in Tux. But when I export it to Gp4 I can open it with Guitar Pro 5, otherwise not.
I think you looked at "License version"
same as:
http://www.tuxguitar.com.ar/license.html
Go to "Help -> About" and you'll see the tuxguitar version.
However if you got it a few days ago, i think you have latest.
Do you have any way to send me the saved .gp5 file ?
You can make contact with me here:
http://www.tuxguitar.com.ar/contact.html
then i'll reply to you. and you'll be able to send me by mail.
because is not a good idea post my or your mail here.