Can’t import messages

Hi,
I’m renovating a website so I need to export messages from old site and import them to the new site.
Old and new site has same plugin version (3.1.1), I can export csv file from old site but when I try to import in new site, it says that csv file is not compatible with this gwolle version.

Both site has same PHP version (5.6) and, as a matter of fact, they run on the same server, they’re just two wordpress installations in 2 different directory of the same server.
Hope you can help.

Thank you