"java.lang.IllegalStateException: getOutputStream() has already been called for this response" when using JSP scriptlet on JBoss

Issue

We have a JSP page that calls an external Java service, which works fine in Borland Enterprise Environment 6.0, on JDK 1.5, but gives us the following error on JBoss:

    java.lang.IllegalStateException: getOutputStream() has already been called for this response
         at org.apache.catalina.connector.Response.getWriter(Response.java:604)
         at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)
         at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)
         at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)
         at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:191)
         at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:118)
         at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:77)
         at org.apache.jsp.crreportsjsp.r_005fdailyBleachingWip_005fcall_jsp._jspService(r_005fdailyBleachingWip_005fcall_jsp.java:166)
         at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
         at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
         at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:387)
         at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
         at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
         at javax.servlet.http.HttpServlet.service(HttpServlet.java:717
         ...

In EAP 7

java.lang.IllegalStateException: UT010006: Cannot call getWriter(), getOutputStream() already called