Why do I receive a Service Unavailable message after running the project GWT?

I am creating a GWT project from the GWT Material official website using maven. I am following the tutorial offered by the site: http://gwtmaterialdesign.github.io/gwt-material-demo/#gettingstarted . Im getting this in the view page:

HTTP ERROR: 503
Problem accessing /index.html. Reason:
Service Unavailable
Powered by Jetty://

I tried all the solution proposed here but I failed to view the project homepage.

There is no error in the eclipse console. but when inspecting the home page im getting this error:

Voice Instead ready.

content.js:29 Object
favicon.ico Failed to load resource: the server responded with a status of 503 (Service Unavailable)
    enter code here

after running the project in the window Developement Mode in the Jetty console next to Developement Mode i have problem with Jetty. i don't know What is jetty and what it allows to do? Im getting this error :

`00:00:16,662  [WARN] Failed startup of context c.g.g.d.s.j.WebAppContextWithReload@3772b95a{/,file:/C:/Users/Mm/eclipse-workspace/com-gwtmaterial-tutorial/target/com-gwtmaterial-tutorial-1.0-SNAPSHOT/,STARTING}{C:\Users\Mm\eclipse-workspace\com-gwtmaterial-tutorial\target\com-gwtmaterial-tutorial-1.0-SNAPSHOT}
<pre>java.util.zip.ZipException: invalid entry size (expected 4178 but got 10926 bytes)
    at java.util.zip.ZipInputStream.readEnd(ZipInputStream.java:384)
    at java.util.zip.ZipInputStream.read(ZipInputStream.java:196)
    at java.util.jar.JarInputStream.read(JarInputStream.java:207)
    at java.util.zip.ZipInputStream.closeEntry(ZipInputStream.java:140)
    at java.util.zip.ZipInputStream.getNextEntry(ZipInputStream.java:118)
    at java.util.jar.JarInputStream.getNextEntry(JarInputStream.java:142)
    at java.util.jar.JarInputStream.getNextJarEntry(JarInputStream.java:179)
    at org.eclipse.jetty.annotations.AnnotationParser.parseJar(AnnotationParser.java:915)
    at org.eclipse.jetty.annotations.AnnotationParser.parse(AnnotationParser.java:831)
    at org.eclipse.jetty.annotations.AnnotationConfiguration$ParserTask.call(AnnotationConfiguration.java:163)
    at org.eclipse.jetty.annotations.AnnotationConfiguration$1.run(AnnotationConfiguration.java:548)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555)
    at java.lang.Thread.run(Thread.java:745)</pre>`

I solved it by following the next step:

1- Close Eclipse.

2- Go to user directory and delete the .m2 directory.

3- Open Elipse.

4- Right click on the project -> Run as -> maven install