what is this ?

(from github.com/MajidSafari)
Exception in thread “AWT-EventQueue-0” java.lang.ClassCastException: sun.java2d.HeadlessGraphicsEnvironment cannot be cast to sun.awt.Win32GraphicsEnvironment
at sun.awt.windows.WToolkit$3.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

(from github.com/marevol)
Need more info.
Fess is not in the stacktrace.

(from github.com/MajidSafari)

when Fess Runing

(from github.com/marevol)

… used by another process.

Kill all Fess processes and then start Fess.