How can a Windows server be a slave to Jenkins running on Linux when there in an error installing the slave-agent.jnlp file?
You have two arguments that are empty:

&lt;application-desc main-class="hudson.remoting.jnlp.Main"&gt;
  &lt;argument&gt;32ba31ca5f150c2b3491802b0b60e56574d970a9e601cebad656a113fe325a85&lt;/argument&gt;
  &lt;argument&gt;FQDNofWindowsSlave&lt;/argument&gt;
  &lt;argument&gt;-workDir&lt;/argument&gt;
  &lt;argument/&gt;
  &lt;argument&gt;-internalDir&lt;/argument&gt;
  &lt;argument/&gt;
  &lt;argument&gt;-url&lt;/argument&gt;
  &lt;argument&gt;http://FQDNofJenkinsServer:8080/&lt;/argument&gt;
&lt;/application-desc&gt;


Your error message has a comma in it:


  BadFieldException[ The field  has an
  invalid value: ,]


Other bad argument error messages on the internet have comma separated lists of bad arguments: 


  BadFieldException[ The field codebase has an invalid value:
  $$codebase,$$codebase]


So I'd guess those two empty arguments are the problem.