Further to my comment, seems post #10 in Issue 66661 that I referred to, has identical error log to yours
!ENTRY org.eclipse.ui 4 0 2014-03-05 21:25:58.203
!MESSAGE Unhandled event loop exception
!STACK 0
java.lang.NoClassDefFoundError: com/android/sdklib/repository/descriptors/IdDisplay
at com.android.sdkuilib.internal.widgets.AvdCreationDialog.createAvd(AvdCreationDialog.java:1180)
at com.android.sdkuilib.internal.widgets.AvdCreationDialog.okPressed(AvdCreationDialog.java:972)
at org.eclipse.jface.dialogs.Dialog.buttonPressed(Dialog.java:472)
at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:624)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:248)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4169)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3758)
at org.eclipse.jface.window.Window.runEventLoop(Window.java:825)
at org.eclipse.jface.window.Window.open(Window.java:801)
...
So it looks like you are using 22.6. Therefore just run AVD Manager from outside Eclipse until they release a 22.6.1 to fix this bug