Java developer to fix a website

We have had someone already look into this and all they could do was suggest what i had already found and had tried on google, i need someone who knows about JAVA SERVERS and JAVA SERVLETS and anything else JAVA related to actually login to the windows server and configure what needs to be done.

General information for the business: Fix a website so it works
Kind of development: Customization of existing program
Description of requirements/functionality: Were currently unable to add certain types of users and tomcat posts this error:

Oct 20, 2015 8:07:19 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.error_jsp._jspService(error_jsp.java:139)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at ClientHandlerServlet.doPost(ClientHandlerServlet.java:90)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:643)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:712)
at org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:683)
at org.apache.jsp.clientprocess_jsp._jspService(clientprocess_jsp.java:120)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:615)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:617)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1778)
at java.lang.Thread.run(Unknown Source)
Specific technologies required: java
OS requirements: Windows
Extra notes: