Common and frequent mistakes, NPEs
Error message "Manifest file missing in module"
When importing an OpenCms module sometimes you get the error message
Error uploading the module [MODULENAME].zip. Manifest file missing in module [PATH_TO_MODULE][MODULENAME].zip.
In most of the cases the problem is, that the zip file you try to import is not the module.zip, but another zip file which includes the real module.zip
(Example from the mailing list: http://www.nabble.com/Workflow-in-v7.0.4-to17319767.html)
HowTo recognise a OpenCms module by its name
OpenCms modules are normally named in java package syntax with the version as suffix.
HowTo use correct content encoding
Quite often people are facing problems with displaying special characters (e.g. German umlauts). Do it like this, and it works:
As OpenCms uses java.util.Properties under the hood ISO-8859-1 will be used by OpenCms to decode the .properties files. So if you use an external editor to edit these files you have to ensure that this editor uses the iso encoding. If you use the internal OpenCms (wysiwyg) editor you should set the encoding property for the property files to ISO-8859-1 (as long as you don't use it as defaultcontentencoding which is UTF-8 by default). (taken from the OpenCms mailinglist - answer from Felix Noz)
Adding permissions for "workplace user" role after adding new site
If you use more than one site (meaning other than the "default site", check out, if you set the permissions on your site's root folder "site/yoursite" for "workplace users" correctly. Just clone the "default site's" permissions.