When an error appears in logs (see Logs) it indicates for which java class you need to increase the level of logging if you want debugging information. You can change logging levels to get additional (debug) information.

You can now alter Log Categories in the Application Server Statistics portlet by clicking that button. This alteration simplifies editing log4j.xml files since it provides a graphical interface, and if you have more than one server, it alters the log levels for all servers.