Hi @redkite
There is a bug in Mailchimp plugin. When Mailchimp is trying to display a notice when Mailchimp is installed but not yet configured, fatal error happens with WooCommerce Admin disabled.
I have already submitted a Pull Request in Mailchimp GitHub: https://github.com/mailchimp/mc-woocommerce/pull/715/files
As soon as the Mailchimp team accepts my commit and release a new version, it will be fixed.
For now, you can try following steps to avoid the fatal error:
1. Disable Mailchimp for WooCommerce
2. Set Disable WooCommerce Admin
to off in the plugin settings
3. Configure Mailchimp for WooCommerce. Complete all steps during the connection wizard.
4. Set Disable WooCommerce Admin
to on in the plugin settings