I have the same problem here on Windows 7 with a local and recent XAMPP installation and OJS 3.0.1
This is the PHP error log:
[15-Dec-2016 13:39:55 Europe/Berlin] PHP Notice: Trying to get property of non-object in D:\xampp\htdocs\ojs\plugins\importexport\native\NativeImportExportPlugin.inc.php on line 133
[15-Dec-2016 13:45:57 Europe/Berlin] PHP Warning: DOMDocument::schemaValidate(): Element '{http://pkp.sfu.ca}revision', attribute 'date_uploaded': '' is not a valid value of the atomic type 'xs:date'. in D:\xampp\htdocs\ojs\lib\pkp\classes\xslt\XMLTypeDescription.inc.php on line 126
[15-Dec-2016 13:45:57 Europe/Berlin] PHP Warning: DOMDocument::schemaValidate(): Element '{http://pkp.sfu.ca}revision', attribute 'date_modified': '' is not a valid value of the atomic type 'xs:date'. in D:\xampp\htdocs\ojs\lib\pkp\classes\xslt\XMLTypeDescription.inc.php on line 126
[15-Dec-2016 13:45:57 Europe/Berlin] PHP Notice: Trying to get property of non-object in D:\xampp\htdocs\ojs\lib\pkp\plugins\importexport\native\filter\SubmissionNativeXmlFilter.inc.php on line 284
[15-Dec-2016 13:45:57 Europe/Berlin] PHP Fatal error: Call to a member function getAttribute() on null in D:\xampp\htdocs\ojs\lib\pkp\plugins\importexport\native\filter\SubmissionNativeXmlFilter.inc.php on line 284
It seems something with the submission file id is wrong (fatal error line 284) but i dont know what. i just uploaded some testdocuments (txt and pdf) for testing.