Hello,
In vertical metrics, my Cap Height and Ascender share the same values. Keeping them both produces an export error.
Will I have any side effect if I delete the Cap Height line instruction? (for instance when setting text alignment in Illustrator)
Thanks! 
All you need is an Ascender metric, as far as I remember. Your vertical metrics should be controlled by the parameters hhea, typo and win for descender and ascender anyway.
I think Jan is talking about the alignment zones and not about the line spacing. I would recommend to set the ascender value to 0 and keep the cap height cause this value is needed in the OS/2 table. If you delete the line, it should be calculated using the H bounding box though, so it shouldn’t create a mess in Illustrator or Indesign when setting alignment on the caps height.
True.
Another way you can circumvent the “overlapping zones” export error: set a scope in the metrics, for example “Case is: Uppercase” for your cap height zone.
This is useful if you have one master in which the zones are separate but another master in which they overlap (or an interpolation where this happens). Setting a scope will circumvent this.
Great thanks! Yes it was about Alignment zones.
Indeed I have no error now (set Cap Height with is Uppercase scope and Ascenders with no scope)
A font needs ascender and cap height. Se setting a scope will not help. But setting the same zone height (or set one to zero).
Don’t get it. If I set the same height to the 2 zones an error blocks the export.
And if I set to 0 one of the two zones (which one?) It will not display in my edit mode while designing.
What Georg means:
After you added a scope to your cap height, add new cap height, this time without a scope, and give it the same position and size values as your ascender.
The if you have two zones that are exactly the same, one is ignored. And all zero width zones are ignored. The problem is when two zones partially overlap.
aahh great thanks! That’s the answer and also why I never got this error before 
Ah, thanks! That’s great to know. Is this mentioned in a tutorial somewhere? I couldn’t find it in the handbook.