C5 v8.1.0: I faced a c5 crash while editing side content over dashboard.

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I faced a c5 crash while editing side content over dashboard.
I was going to publish my changes over the publish button (left side bar) and then I got the following error:

The cache directory must be published under the webroot (or you can set the concrete.cache.directory_relative configuration option)

Can anyone help, how to get my C5 8.1.0 website back and running?

Resipisco