After importing 3 xml-files into the mx-application (java-call; statement Core.storeFileDocumentContent) I physically moved the 3 file from one folder in explorer (same java-call; statement file.renameTo). That worked fine. Subsequently I tried to import 4 html-files using another java-call the same way. Import into mx was successful but moving to another physical folder failed. Unless I did a refreshment of the screen and imported the selection line-by-line (although there were no passing data!). Very stange! Maybe there's something locked that should be released? No exceptions or whatsoever in stack-trace other than user defined message.