Q: Error accessing /solr/admin/. Reason: Severe errors in solr configuration I'm getting an issue that I really can't find out why it's happening. I'm using the "example" package from SOLR website on a DEV environnement. I've change the schemal.xml to fit my needs and at this point, everything works fine.
To have it works on my Staging server, I've simply "tar" the whole "example" package with my changes and send it on the server. So it's exactly the same config file, ports, etc. 
Un-tar it and put it in my website folder. I've start the solr instance using: nohup java -jar start.jar &
At this point I don't see any error in shell, but when I access it through localhost:8983/solr, I have the following error (at the bottom)
The JAVA version on that server is almost the same: "1.7.0_21" on Staging, "1.7.0_03" on DEV.
Does anybody have any idea ?
HTTP ERROR 500

Problem accessing /solr/. Reason:

Severe errors in solr configuration.

Check your log files for more detailed information on what may be wrong.

If you want solr to continue after configuration errors, change: 

 <abortOnConfigurationError>false</abortOnConfigurationError>

in solr.xml

-------------------------------------------------------------
org.apache.solr.common.SolrException: Error loading class 'solr.VelocityResponseWriter'
    at org.apache.solr.core.SolrResourceLoader.findClass(SolrResourceLoader.java:389)
    at org.apache.solr.core.SolrCore.createInstance(SolrCore.java:425)
    at org.apache.solr.core.SolrCore.createInitInstance(SolrCore.java:447)
    at org.apache.solr.core.SolrCore.initPlugins(SolrCore.java:1556)
    at org.apache.solr.core.SolrCore.initPlugins(SolrCore.java:1550)
    at org.apache.solr.core.SolrCore.initPlugins(SolrCore.java:1583)
    at org.apache.solr.core.SolrCore.initWriters(SolrCore.java:1466)
    at org.apache.solr.core.SolrCore.<init>(SolrCore.java:556)
    at org.apache.solr.core.CoreContainer.create(CoreContainer.java:463)
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:316)
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:207)
    at     org.apache.solr.core.CoreContainer$Initializer.initialize(CoreContainer.java:130)
    at org.apache.solr.servlet.SolrDispatchFilter.init(SolrDispatchFilter.java:94)
    at org.mortbay.jetty.servlet.FilterHolder.doStart(FilterHolder.java:97)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:713)
    at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
    at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1282)
    at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:518)
    at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:499)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
    at     org.mortbay.jetty.handler.ContextHandlerCollection.doStart(ContextHandlerCollection.java:15    6)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
    at org.mortbay.jetty.Server.doStart(Server.java:224)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.xml.XmlConfiguration.main(XmlConfiguration.java:985)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at     sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.mortbay.start.Main.invokeMain(Main.java:194)
    at org.mortbay.start.Main.start(Main.java:534)
    at org.mortbay.start.Main.start(Main.java:441)
    at org.mortbay.start.Main.main(Main.java:119)
Caused by: java.lang.ClassNotFoundException: solr.VelocityResponseWriter
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
    at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:789)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:266)
    at org.apache.solr.core.SolrResourceLoader.findClass(SolrResourceLoader.java:373)
    ... 37 more


A: Make sure you have the apache-solr-velocity-XX.jar and all its dependencies in your Core lib for the class to be able to load.
VelocityResponseWriter - Check the versions accordingly.
velocity-1.6.1.jar 
velocity-tools-2.0-beta3.jar 
commons-beanutils-1.7.0.jar 
commons-collections-3.2.1.jar

