Since you aren't using any deployment descriptors, I would guess that jCalendar.jar has a Main-Class entry in its manifest.
The default behavior for Java EE 5 deployment in that situation is to assume that the jCalendar.jar is an app client jar.
The way to make it clear to a Java EE 5 server, like GlassFish, is to add an application.xml file to you enterprise application that does not list jCalendar.jar anywhere.
Note: once you add an application.xml file, it must be complete and describe all of the various Java EE modules that are part of your app.
vbk
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