I have found the error by comparing my permissions.xml file with this one
In this file the permissions tag is:
Another problem with my file is that the classname tag should be instead class-name.
Perhaps it would be a good idea to correct the example given in the paragraph “5.2.2. Defining Policies in the Deployment” at https://access.redhat.com/documentation/en/red-hat-jboss-enterprise-application-platform/version-7.0/how-to-configure-server-security/#java_security_manager