I found this error log after wroot pointed out where to find them.
Jun 19, 2012 11:16:34 AM org.jivesoftware.spark.util.log.Log error
SEVERE: Error sending message
java.lang.NullPointerException
at java.util.Hashtable.put(Unknown Source)
at javax.swing.text.SimpleAttributeSet.addAttribute(Unknown Source)
at javax.swing.text.StyleConstants.setForeground(Unknown Source)
at org.jivesoftware.spark.ui.TranscriptWindow.insertMessage(TranscriptWindow.java: 190)
at org.jivesoftware.spark.ui.rooms.ChatRoomImpl.sendMessage(ChatRoomImpl.java:278)
at org.jivesoftware.spark.ui.rooms.ChatRoomImpl.sendMessage(ChatRoomImpl.java:264)
at org.jivesoftware.spark.ui.rooms.ChatRoomImpl.sendMessage(ChatRoomImpl.java:239)
at org.jivesoftware.spark.ui.ChatRoom.checkForEnter(ChatRoom.java:706)
at org.jivesoftware.spark.ui.ChatRoom.access$300(ChatRoom.java:89)
at org.jivesoftware.spark.ui.ChatRoom$3.keyPressed(ChatRoom.java:335)
at java.awt.AWTEventMulticaster.keyPressed(Unknown Source)
at java.awt.Component.processKeyEvent(Unknown Source)
at javax.swing.JComponent.processKeyEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(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)
I did use full installer.
Does this help?