Hi,
I am not quite sure what is happening there, but PDFCreator can't create xfdl files, is this the intended output format, or the input? The version you are using is rather old, if you can update to PDFCreator 3.2.2 we will be able to provide better support.
Please set the logging level to "trace" in the PDFCreator application settings, reproduce the error and send us the log to support(at)pdfforge.org
Best regards
Robin