Beginner on Glyphs Mini encountering kerning problems

Hi there - I’m a newcomer to Glyphs Mini just trying to finish off my first font, and kerning is giving me a few headaches. When I try to export the font, I get an error message - ‘Illegal kerning group name - the glyph Z has illegal character in the kerning group name: ‘@MMK_L_’ (at pos: 0)’. There is no group with that name in the Kerning window - what does this mean and how do I fix it?

Also, the Glyphs Mini handbook says there should be a minus sign at the bottom left of the kerning window - instead, there’s something that looks like an ‘Re’ with a line through it. What is this button?

Open your Z and set the kerning groups. Best to write Z in both Kerning Group field:


I suspect that there was indeed an unusual (perhaps invisible or space) char in the left field.

Thank you very much! It turns out, I had invisible spaces everywhere in the kerning - took a while, but I have successfully exported!

(Also: The button at the bottom of the kerning panel that looks like an ‘Re’ - what does that actually do?j

This is how it is supposed to look:
Bildschirmfoto 2021-04-14 um 23.15.04
The “Re” is the title of the button that isn’t supposed to be visible.