[xwiki-users] X11 needed on the server?

Hello users, we are fighting with a spurious error occurring in our system: org.apache.velocity.exception.MethodInvocationException: Invocation of method 'getWidth' in class com.xpn.xwiki.plugin.image.ImagePluginAPI threw exception java.lang.NoClassDefFoundError: Could not initialize class sun.awt.X11.XToolkit @ Coll_Group_IREM-INRP- AcademiedeLyon.Introductionalamediatrice610,36? at org .apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java: 300) at org .apache .velocity.runtime.parser.node.ASTReference.execute(ASTReference.java: 203) at where basically it seems that an X11 connection is wished even though there's none (on a SuSE linux with a Sun Java). What is the normal way in Java (and on my tomcat) to avoid X11 connections and still get some image services (such as getWidth) ?? thanks in advance paul