Steps to replicate

1. Install Confluence 5.8.16
2. Create a new page and save the page
3. Install Confluence Source editor
4. Click edit on the new page and then find for '<>' to open the source editor
5. Add the following code

   <ac:structured-macro ac:name="code"><ac:parameter ac:name="title">1st step source code</ac:parameter><ac:parameter ac:name="linenumbers">true</ac:parameter><ac:parameter ac:name="language">xml</ac:parameter><ac:parameter ac:name="collapse">true</ac:parameter><ac:plain-text-body><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
   <config charset="UTF-8">
     
     <!-- get the page -->
      <var-def name="profile_page_url">
        <script return="pPage">
            <![CDATA[
              pPage = org.apache.commons.httpclient.util.URIUtil.encodeQuery(profile_page.toString());
            ]]]]><![CDATA[>
        </script>
      </var-def>
     
      <var-def name="profilePage">
         <html-to-xml>
       		<http url="${profile_page_url}"/>
         </html-to-xml>
      </var-def>
        
        <var-def name="company_name_link">
          <xpath expression="//*/div[1]/div[2]/div[2]/h3[1]/a[1]/@href">
                 <template>${profilePage}</template>
             </xpath>
        </var-def>
        
      <export include-original-data="true" external-url="${profile_page_url}">  
       <single-column name="company_name_link" value="${company_name_link}" xpath="//*/div[1]/div[2]/div[2]/h3[1]/a[1]/@href"/>      
      </export>
   	
   </config>]]></ac:plain-text-body></ac:structured-macro>
   

Observed behaviour
The user won't be able to save the page. They will be seeing the following error:

Expected Behaviour
User should be able to save the page