Apple - Photoshop on mac "could not save [file] because write access was not granted"

After some trial and error, I tracked it down to the file being selected in Finder.

It seems like when Finder is displaying a preview of a PSD, it locks the file.

It seems to only happen in this view mode:

Selecting another file in Finder, or switching view mode, or closing the finder window, all prevent this error.

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So while Finder is like this, the file won't save:

Clicking off it frees it for saving:

As does switching to this view mode to one that doesn't show a preview:

IMHO the problem is caused by the SMB protocol, then in fact there are some ”strange process” opened by the Finder. I changed the server protocol for AFP and everything works well. In my case I changed shared folder’s settings in Server app ver. 4.1.5, but this works is mac os x System Preferences as well. The eventual disadvantage – there is no connection of PCs to the server.