The exception is saying that this class:
org.apache.solr.client.solrj.SolrServerException
cannot be found in the webapp's classpath.
According to the findjar service, that class is defined solr-core-1.3.0.jar
and solr-solrj-1.3.0.jar
. You may need to update your build procedure to include one of those JARs in the WAR file. (If you are using Maven, add a runtime dependency for the relevant artifact to the POM file ...)