The new release of Oracle Application Express 4.1 will be installed into a new schema in your database. The name of this schema is 'APEX_040100'. Unfortunately, the Installation Guide for Oracle Application Express 4.1 references a schema name of 'APEX_041000'. This is incorrect. For any example code (e.g., creation of Network ACL) which references APEX_041000, simply replace it first with APEX_040100.
Hopefully this error is short-lived, as I have reported this error to our documentation team and requested that they correct this in the hosted documentation. If you're reading this blog post a month from now and you don't see any reference to the incorrect APEX_041000, then the problem has been resolved.
Important Update: As of August 26, 2011, this problem is now resolved. This is the beauty and flexibility of online help and documentation.