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I believe it's a good idea to give more information about the $Config['UserFilesPath']. I myself often had a problem configuring it, then I wrote a small howto: http://www.fckeditor.net/forums/viewtopic.php?f=6&t=4583
More information about the xml (request and response) format. xsd o dtd will be desirable.
"The XML Response looks similar to this:" it's insufficient.