The error is caused by a SQL error. It happened to me recently and found a mistake in a line responsible for the insertion of documents in the table posts. This error appears in the file \ wp-admin \ includes \ file.php (line 280) and in the file \ wp-admin \ includes \ import.php (line 63) (responsible for the import of xml) and despite the SQL script insertion arise later, swfupload returns this error. This can be caused by file name or any other reason. It happened to me, I hope I can help …
