Language tag error

Hello, I am new to Glyphs and while on my trial period I have been facing this error quite frequently. Any help would be highly appreciated.

The steps leading to it are as follows:

  1. Font works perfectly, and I can export as expected
  2. Without me changing anything, a red exclamation mark appears close to Features
  3. When trying to export, I get an error saying ‘Expected language tag
    Found in: prefix ‘Languagesystems’, line 5.’

What version of Glyphs do you have?

Try the latest beta please. Go to Glyphs > Preferences > Updates, activate both checkboxes and press the Update button.