Access Denied even to SharePoint Administrator

Message
Access Denied.
Editing/Settings are NOT enabled even for administrators.

Context
SharePoint Site Collection, maybe after backup/restore a site collection

Explanation
The Site Collection is in "Read only" mode. Maybe due to a stsadm backup brutally interrupted.

Solution
Open the SharePoint Central Administration. Under Application Magement, click on the "Configure quotas and locks" link. Than have a look under the section "Site Lock Information" and be sure it is selected "Not locked" option.