WebClient error

Hello

When I want to connect to the WebClient an erro occured : After enter login and password -- > an Html page with this message Error !

I attach the webclient log :

----------------General Information----------------
Product = OpManager Version x.x
User Name = admin
BE Server Name = SHERLOCK
FE Server Name = 167.0.4.11
OS Name = Windows XP
OS Version = 5.1
OS Architecture = x86
Java Version = 1.5.0
Java Vendor = Sun Microsystems Inc.
Java Specification = Java Platform API Specification
Java Specification version = 1.5
Java VM name = Java HotSpot(TM) Client VM
Java VM information = mixed mode
Java Compiler = null
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Messages on lundi 25 juillet 2005
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Exception in thread "Thread-8" java.lang.InstantiationError: Unable to create a new Instance of class "com.adventnet.me.opmanager.client.accpanel.SeverityAlarmChart" corresponding to card "SeverityChart". Encountered exception java.lang.NoClassDefFoundError. Exception Message : org/jfree/ui/ExtensionFileFilter
at com.adventnet.beans.panels.CardPanel.getCardComponent(CardPanel.java:400)
at com.adventnet.beans.panels.CardPanel.getComponent(CardPanel.java:338)
at com.adventnet.beans.panels.CardPanel.showCard(CardPanel.java:236)
at com.adventnet.beans.panels.CardPanel.showCard(CardPanel.java:199)
at com.adventnet.me.opmanager.client.accpanel.ACCPanel.initUserProps(ACCPanel.java:536)
at com.adventnet.me.opmanager.client.accpanel.ACCPanel.init(ACCPanel.java:116)
at com.adventnet.me.opmanager.client.accpanel.ACCPanel.<init>(ACCPanel.java:443)
at com.adventnet.me.opmanager.client.accpanel.ACCPanel.getInstance(ACCPanel.java:63)
at com.adventnet.me.opmanager.client.accpanel.OpManagerACCPanel.<init>(OpManagerACCPanel.java:21)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at java.lang.Class.newInstance0(Unknown Source)
at java.lang.Class.newInstance(Unknown Source)
at com.adventnet.nms.startclient.MainPanel.run(MainPanel.java:582)
at com.adventnet.nms.startclient.MainPanel.init(MainPanel.java:432)
at com.adventnet.nms.startclient.NmsMainFrame.init(NmsMainFrame.java:75)
at com.adventnet.nms.startclient.NmsMainApplet.run(NmsMainApplet.java:330)
at java.lang.Thread.run(Unknown Source)