Ok, I think I've pointed the problem.
When I started Kstars/Ekos, I have been to the capture module, and the document folder was already set, so I didn't open the file brower to select it. I think the consequence is kstars hasn't "unlock" the osx security on the document folder or something like that... As soon as I've opened the folder to select one (or even reselect the same after that) no more problems it has just ruined 45 minutes of shoots astro life ......

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