This issue was originally marked as duplicate of issue 157538, that is already resolved. This issue is still valid, so this seems to be another issue, but it might be related.

Build: NetBeans IDE 6.8 M2 (Build 200910071658)
VM: Java HotSpot(TM) Client VM, 11.2-b01, Java(TM) SE Runtime Environment, 1.6.0_12-b04
OS: Windows Vista, 6.0, x86

User Comments:
smsmithee: tried to open properties on a maven project.

GUEST: on a jee5 maven webapp project, right-click, properties

tsromney: Trying to access project properties from a newly created maven project

neilg: Selected "Properties" from the context menu on a maven webapp

ben_kelley: view project properties for a maven project

navneet: trying to see the properties of a maven project. this was working in netbeans 6.5

ecastro: Opening properties for an old maven project

tsromney: Trying to edit project properties for a newly created maven project

ezorro: Project Properties won't open (not visible). Even IDE restart does not fix the problem.

GUEST: I was trying to view properties for a project.

-------------------------------------------------------------------------------
>Log Session: Sunday, July 19, 2009 12:08:32 AM MST
>System Info: 
  Product Version         = NetBeans IDE 6.7 (Build 200906241340)
  Operating System        = Windows XP version 5.1 running on x86
  Java; VM; Vendor        = 1.6.0_13; Java HotSpot(TM) Client VM 11.3-b02; Sun Microsystems Inc.
  Runtime                 = Java(TM) SE Runtime Environment 1.6.0_13-b03
  Java Home               = C:\Program Files\Java\jdk1.6.0_13\jre
  System Locale; Encoding = en_US (nb); Cp1252
  Home Directory          = C:\Documents and Settings\jhonce
  Current Directory       = C:\Program Files\NetBeans 6.7
  User Directory          = C:\Documents and Settings\jhonce\.netbeans\6.7
  Installation            = C:\Program Files\NetBeans 6.7\nb6.7
                            C:\Program Files\NetBeans 6.7\ide11
                            C:\Program Files\NetBeans 6.7\java2

GUEST: select project, right click, properties... crashhh

GUEST: Netbeans Options does not load.
Have not changed anything except added a 4 th monitor 1900x1200. Subsequently, properties does not work either.

GUEST: Right click on a project - select "properties"

GUEST: Tried to open Project Poperties Editor.

GUEST: right-click on maven project and choose "properties"

GUEST: I just click in 'Force Run Garbage Collector' option of memory display and the error occur.

GUEST: right-click on project, click "properties"

GUEST: Open Project didn't work

onmomo: I did right click on a maven project and choose properties

japod: Maven based project:

Run junit tests
Was trying to find a string in the output window -- a dialog poped up, where i filled the string, but nothing happened afterwards, tried once more, but the same result

Then went to another project and tried to open Project properties dialog, and for about a minut NB has not been responsing, then this "Report problem" dialog poped up, so i am writing this...

pdeville: when using maven plugin it is impossible to debug or run the project 

NetBeans: Executing '/local/softs/maven/2.1.0/bin/mvn -Dexec.classpathScope=runtime -Dexec.args=-classpath %classpath com.goodyear.storetech.swing.Main -Dexec.executable=/local/softs/java/1.6.0_10/bin/java -Dnetbeans.execution=true --fail-fast process-classes exec:java'
NetBeans:      JAVA_HOME =/local/softs/java/1.6.0_10
Scanning for projects...
------------------------------------------------------------------------
Building Storetech Swing client Application
   task-segment: [process-classes, exec:java]
------------------------------------------------------------------------
[resources:resources]
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
Copying 1 resource
Copying 1 resource
[compiler:compile]
Nothing to compile - all classes are up to da

jonycus: Ma gonite se u trista picke materine



Stacktrace: 
java.lang.IllegalStateException: Current thread has already started a transaction
        at org.netbeans.modules.xml.xam.AbstractModel.startTransaction(AbstractModel.java:346)
        at org.netbeans.modules.xml.xam.AbstractModel.startTransaction(AbstractModel.java:341)
        at org.netbeans.modules.maven.api.customizer.ModelHandle.<init>(ModelHandle.java:127)
        at org.netbeans.modules.maven.api.customizer.ModelHandle.<init>(ModelHandle.java:68)
        at org.netbeans.modules.maven.api.customizer.ModelHandle$AccessorImpl.createHandle(ModelHandle.java:110)
        at org.netbeans.modules.maven.customizer.CustomizerProviderImpl.init(CustomizerProviderImpl.java:255)