How to reproduce:
1) mount any empty filesystem and convert it to a web 
module.
2) Create new JSP page
3) Add any tag library to this project (I've used a 
standard library from the Repository)
4) type in Source editor following line:
<%@taglib uri="/standard" prefix="test" %>
5) Now try to delete WEB-INF node in the explorer. It will 
throw an exception (you can find it at the end of this 
description).
6) Delete the line you typed before and try to delete WEB-
INF node again. Exactly the same exception will be thrown.

Now it's not possible to delete this node even you restart 
IDE.

-----------------------------------------------------
Fri Mar 22 15:43:36 MSK 2002: 
org.openide.filesystems.FSException:  Cannot delete file 
WEB-INF/lib/js.jar in C:\Test.
org.openide.filesystems.FSException: Cannot delete file WEB-
INF/lib/js.jar in C:\Test.
        at org.openide.filesystems.FSException.io
(FSException.java:78)
        at org.openide.filesystems.LocalFileSystem.delete
(LocalFileSystem.java:321)
        at org.netbeans.core.ExLocalFileSystem.delete
(ExLocalFileSystem.java:75)
        at 
org.openide.filesystems.LocalFileSystem$Impl.delete
(LocalFileSystem.java:659)
        at org.openide.filesystems.AbstractFileObject.delete
(AbstractFileObject.java:480)
        at 
org.netbeans.modules.web.context.DefaultDataObject.handleDel
ete(LibJarObject.java:152)
        at 
org.netbeans.modules.web.context.LibJarObject.handleDelete
(LibJarObject.java:72)
        at org.openide.loaders.DataObject$2.run
(DataObject.java:524)
        at 
org.openide.filesystems.EventControl.runAtomicAction
(EventControl.java:89)
        at 
org.openide.filesystems.FileSystem.runAtomicAction
(FileSystem.java:388)
        at org.openide.loaders.DataObject.delete
(DataObject.java:522)
        at 
org.netbeans.modules.web.context.WebInfObject.handleDelete
(WebInfObject.java:148)
        at org.openide.loaders.DataObject$2.run
(DataObject.java:524)
        at 
org.openide.filesystems.EventControl.runAtomicAction
(EventControl.java:89)
        at 
org.openide.filesystems.FileSystem.runAtomicAction
(FileSystem.java:388)
        at org.openide.loaders.DataObject.delete
(DataObject.java:522)
        at org.openide.loaders.DataNode.destroy
(DataNode.java:219)
        at org.openide.nodes.FilterNode.destroy
(FilterNode.java:399)
        at org.openide.nodes.FilterNode.destroy
(FilterNode.java:399)
        at 
org.openide.explorer.ExplorerActions$DeleteActionPerformer$D
estroyAtomic.invoke(ExplorerActions.java:527)
        at $Proxy4.run(Unknown Source)
        at 
org.openide.filesystems.EventControl.runAtomicAction
(EventControl.java:89)
        at 
org.openide.filesystems.FileSystem.runAtomicAction
(FileSystem.java:388)
        at 
org.openide.explorer.ExplorerActions$DestroyInvoker.run
(ExplorerActions.java:568)
        at 
org.openide.explorer.ExplorerActions$DeleteActionPerformer.d
oDestroy(ExplorerActions.java:494)
        at 
org.openide.explorer.ExplorerActions$DeleteActionPerformer.p
erformAction(ExplorerActions.java:463)
        at 
org.openide.util.actions.CallbackSystemAction.performAction
(CallbackSystemAction.java:109)
        at 
org.openide.util.actions.CallableSystemAction.actionPerforme
d(CallableSystemAction.java:69)
        at org.netbeans.core.ModuleActions$1.run
(ModuleActions.java:105)
        at org.openide.util.Task.run(Task.java:152)
[catch] at 
org.openide.util.RequestProcessor$ProcessorThread.run
(RequestProcessor.java:622)