This bug was originally marked as duplicate of bug 166513, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE 6.9 (Build 201006101454)
VM: Java HotSpot(TM) 64-Bit Server VM, 16.0-b13, Java(TM) SE Runtime Environment, 1.6.0_18-b07
OS: Linux

User Comments:
GUEST: Started netbeans.

GUEST: This happened when I started netbeans. I closed the open project while it was loading

ianmarshall: I was stepping over an "if" statement in debug mode.

mithridates: Tried to open "Servers"-node while NB was starting up.

jbecicka: while dubugging netbeans ide

GUEST: debugging app

GUEST: Debugging a NetBeans Platform application

GUEST: debugging remote java application

zaiboot: I was debugging a web app

GUEST: Perhaps occurred while debugging, but not sure

GUEST: running debugger

dethmaster: I was making a comment in a pom.xml for a project. When I closed the comment off it threw this exception.

vkvashin: I added a watch (to an instance of ConcurrentHashMap), set a breakpoint... on 3-rd - 4-th stop on this breakpoint (watch should be valid at that point), i tried to expand the map - exception occurred

aldobrucale: After "Apply Code Changes" in java

duncank: Debugging a swing app client EE project.  A breakpoint was triggered.

tboerkel: Editing

GUEST: Debugging web application, two lines of code and hit apply changes to code.




Stacktrace: 
java.lang.IndexOutOfBoundsException: Index: 2, Size: 0
   at java.util.ArrayList.RangeCheck(ArrayList.java:547)
   at java.util.ArrayList.remove(ArrayList.java:387)
   at org.openide.explorer.view.VisualizerChildren.removed(VisualizerChildren.java:256)
   at org.openide.explorer.view.VisualizerEvent$Removed.run(VisualizerEvent.java:134)
   at org.openide.util.Mutex.readAccess(Mutex.java:365)
   at org.openide.util.Mutex$1R.run(Mutex.java:1307)