Upgrade 3.70 - 4.00 Application startup exception seven spikes core

Hi

I upgraded a site from 3.70 to 4.00.

Its a single shop.

Everything runs fine until I push Update plugin list then I get this error:

Application startup exception: System exception:Plugin 'seven spikes core' Acces to path '......./plugins/bin/sevenspikes.nop.plugins.core.dll' is denied.

In warnings all the right permissions are "green".

The right permissions are granted to all files and folders.

What can I check?

Br
Tommy