Eclipse Plugin stopped working

Hello Group,

I am using the GWT now for some months, trying around and coding on a
certain project. But from the one day to the other the project isn't
compiling anymore on my Eclipse environment, it works on another
environment thought, which means (in my eyes), it shouldn't be a
problem caused by the code itself.
When I want to start the project via "Start As: Google Webapplication"
I get following error:

Unable to start embedded HTTP server
java.lang.RuntimeException: Unable to locate the App Engine agent.
Please use dev_appserver, KickStart, or set the jvm flag: "-
javaagent:<sdk_root>/lib/agent/appengine-agent.jar"
at
com.google.appengine.tools.development.DevAppServerFactory.testAgentIsInstalled(DevAppServerFactory.java:
102)
at
com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:
77)
at
com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:
38)
at
com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:
79)
at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:377)
at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:938)
at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:690)
at com.google.gwt.dev.DevMode.main(DevMode.java:251)
Caused by: java.lang.NoClassDefFoundError:
com.google.appengine.tools.development.agent.AppEngineDevAgent
at
com.google.appengine.tools.development.DevAppServerFactory.testAgentIsInstalled(DevAppServerFactory.java:
98)
...7 more

--------------

Trying to compile this error:

[ERROR] Failure while parsing XML
org.xml.sax.SAXNotSupportedException: http://apache.org/xml/features/nonvalidating/load-external-dtd
at gnu.xml.stream.SAXParserFactory.setFeature(libgcj.so.90)
at com.google.gwt.dev.util.xml.ReflectiveParser
$Impl.parse(ReflectiveParser.java:320)
at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.access
$100(ReflectiveParser.java:48)
at
com.google.gwt.dev.util.xml.ReflectiveParser.parse(ReflectiveParser.java:
398)
at
com.google.gwt.dev.cfg.ModuleDefLoader.nestedLoad(ModuleDefLoader.java:
257)
at com.google.gwt.dev.cfg.ModuleDefLoader
$1.load(ModuleDefLoader.java:169)
at
com.google.gwt.dev.cfg.ModuleDefLoader.doLoadModule(ModuleDefLoader.java:
283)
at
com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(ModuleDefLoader.java:
141)
at com.google.gwt.dev.Compiler.run(Compiler.java:184)
at com.google.gwt.dev.Compiler$1.run(Compiler.java:152)
at
com.google.gwt.dev.CompileTaskRunner.doRun(CompileTaskRunner.java:87)
at
com.google.gwt.dev.CompileTaskRunner.runWithAppropriateLogger(CompileTaskRunner.java:
81)
at com.google.gwt.dev.Compiler.main(Compiler.java:159)
[ERROR] Unexpected error while processing XML
com.google.gwt.core.ext.UnableToCompleteException: (see previous log
entries)
at com.google.gwt.dev.util.xml.ReflectiveParser
$Impl.parse(ReflectiveParser.java:351)
at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.access
$100(ReflectiveParser.java:48)
at
com.google.gwt.dev.util.xml.ReflectiveParser.parse(ReflectiveParser.java:
398)
at
com.google.gwt.dev.cfg.ModuleDefLoader.nestedLoad(ModuleDefLoader.java:
257)
at com.google.gwt.dev.cfg.ModuleDefLoader
$1.load(ModuleDefLoader.java:169)
at
com.google.gwt.dev.cfg.ModuleDefLoader.doLoadModule(ModuleDefLoader.java:
283)
at
com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(ModuleDefLoader.java:
141)
at com.google.gwt.dev.Compiler.run(Compiler.java:184)
at com.google.gwt.dev.Compiler$1.run(Compiler.java:152)
at c
---------

I'm not yet very advanced in Java / GWT but I'd like to keep on
writing on my project and Eclipse served well as it just did what it
should have done with an click on a button, so I'd really like to know
how I can fix these problems.
I hope someone can help me here

Thanks
Michael

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