title: java.lang.LinkageError: loader constraint violation in Grails project
body: <p>I've built a Grails project with POI (include poi-3.7 and poi-ooxml-3.7). I've added these 2 external libraries to dependencies block in BuildConfig.groovy file of my project. There's nothing strange when I compiled it. But when I called the command "run-app" for that project, an error occured with below stacktrace:  </p>
  
  <pre><code>Base Directory: &lt;path-to-my-project&gt;
  Resolving dependencies...
  Dependencies resolved in 5546ms.
  Running script D:\_TOOLS\STS\grails-1.3.5\scripts\RunApp.groovy
  Environment set to development
  Running Grails application..
  2011-05-23 18:51:01,225 [main] ERROR context.GrailsContextLoader  - Error executing bootstraps: java.lang.LinkageError: loader constraint violation: loader (instance of &lt;bootloader&gt;) previously initiated loading for a different type with name "org/w3c/dom/DOMConfiguration"
  org.codehaus.groovy.runtime.InvokerInvocationException: java.lang.LinkageError: loader constraint violation: loader (instance of &lt;bootloader&gt;) previously initiated loading for a different type with name "org/w3c/dom/DOMConfiguration"
      at grails.spring.BeanBuilder.invokeBeanDefiningClosure(BeanBuilder.java:723)
      at grails.spring.BeanBuilder.beans(BeanBuilder.java:573)
      at grails.spring.BeanBuilder.invokeMethod(BeanBuilder.java:519)
      at org.grails.tomcat.TomcatServer.start(TomcatServer.groovy:212)
      at grails.web.container.EmbeddableServer$start.call(Unknown Source)
      at RunApp$_run_closure5_closure12.doCall(RunApp:158)
      at RunApp$_run_closure5_closure12.doCall(RunApp)
      at _GrailsSettings_groovy$_run_closure10.doCall(_GrailsSettings_groovy:280)
      at _GrailsSettings_groovy$_run_closure10.call(_GrailsSettings_groovy)
      at RunApp$_run_closure5.doCall(RunApp:149)
      at RunApp$_run_closure5.call(RunApp)
      at RunApp.runInline(RunApp:116)
      at RunApp.this$4$runInline(RunApp)
      at RunApp$_run_closure1.doCall(RunApp:59)
      at RunApp$_run_closure1.doCall(RunApp:33)
      at gant.Gant$_dispatch_closure5.doCall(Gant.groovy:381)
      at gant.Gant$_dispatch_closure7.doCall(Gant.groovy:415)
      at gant.Gant$_dispatch_closure7.doCall(Gant.groovy)
      at gant.Gant.withBuildListeners(Gant.groovy:427)
      at gant.Gant.this$2$withBuildListeners(Gant.groovy)
      at gant.Gant$this$2$withBuildListeners.callCurrent(Unknown Source)
      at gant.Gant.dispatch(Gant.groovy:415)
      at gant.Gant.this$2$dispatch(Gant.groovy)
      at gant.Gant.invokeMethod(Gant.groovy)
      at gant.Gant.executeTargets(Gant.groovy:590)
      at gant.Gant.executeTargets(Gant.groovy:589)
  
  Caused by: java.lang.LinkageError: loader constraint violation: loader (instance of &lt;bootloader&gt;) previously initiated loading for a different type with name "org/w3c/dom/DOMConfiguration"
      at java.lang.Class.getDeclaredMethods0(Native Method)
      at java.lang.Class.privateGetDeclaredMethods(Class.java:2427)
      at java.lang.Class.getDeclaredMethods(Class.java:1791)
      at java.security.AccessController.doPrivileged(Native Method)
      at org.codehaus.groovy.util.LazyReference.getLocked(LazyReference.java:46)
      at org.codehaus.groovy.util.LazyReference.get(LazyReference.java:33)
      at grails.spring.DynamicElementReader.invokeMethod(DynamicElementReader.groovy:121)
      ... 26 more  
  </code></pre>
  
  <p>And here is my configuration:  </p>
  
  <pre><code>dependencies {  
          provided ('com.oracle:ojdbc6_g:11.2.0.1.0')  
          runtime ('org.apache.poi:poi:3.7', 'org.apache.poi:poi-ooxml:3.7')  
      }  
  </code></pre>
  
  <p>How can I do to make solve this? Thank you so much!</p>