We are seeing the exact same issue with importing classes from 1.9 to 2.3.4 on Windows servers, and did not have this issue on 2.3.3 as I imported a number of classes without this error. In my testing it appears to be an issue in the import during the conversion process after the "Destination" step with all files in the "course_files" directory of the backup .zip file. The import fails on each file in that directory, and as I remove each one that causes the error from the .zip and try again, the next file in line then causes the same error.
Once I remove all files form course_files in the export .zip, the import process completes with no errors. So this is an ok work around for classes with few course_files, but most of ours have a number of files and this will break all links to them in the course, and we have upload the removed files and fix all of the links after the fact.
Here is an example of our error message and stack trace:
Error code: file_invalid_path
$a contents: \\SERVERNAME.DOMAIN\MOODLEDATA$/temp/backup/d059109be15b84a9650fc97a9e6c4e4b/course_files\2013-ESL_016-What_did_you_do_last_weekend-Jan._14_2013.docx
- line 1215 of \backup\converter\moodle1\lib.php: moodle1_convert_exception thrown
- line 1302 of \backup\converter\moodle1\lib.php: call to moodle1_file_manager->migrate_file()
- line 578 of \backup\converter\moodle1\handlerlib.php: call to moodle1_file_manager->migrate_directory()
- line 566 of \backup\converter\moodle1\handlerlib.php: call to moodle1_files_handler->migrate_course_files()
- line 312 of \backup\converter\moodle1\handlerlib.php: call to moodle1_files_handler->process()
- line 371 of \backup\converter\moodle1\lib.php: call to moodle1_root_handler->on_root_element_start()
- line 756 of \backup\converter\moodle1\lib.php: call to moodle1_converter->path_start_reached()
- line 228 of \backup\util\xml\parser\processors\simplified_parser_processor.class.php: call to moodle1_parser_processor->notify_path_start()
- line 102 of \backup\util\xml\parser\processors\simplified_parser_processor.class.php: call to simplified_parser_processor->process_pending_startend_notifications()
- line 92 of \backup\util\xml\parser\processors\progressive_parser_processor.class.php: call to simplified_parser_processor->process_chunk()
- line 169 of \backup\util\xml\parser\progressive_parser.class.php: call to progressive_parser_processor->receive_chunk()
- line 212 of \backup\util\xml\parser\progressive_parser.class.php: call to progressive_parser->publish()
- line ? of unknownfile: call to progressive_parser->start_tag()
- line 158 of \backup\util\xml\parser\progressive_parser.class.php: call to xml_parse()
- line 137 of \backup\util\xml\parser\progressive_parser.class.php: call to progressive_parser->parse()
- line 150 of \backup\converter\moodle1\lib.php: call to progressive_parser->process()
- line 129 of \backup\converter\convertlib.php: call to moodle1_converter->execute()
- line 209 of \backup\util\helper\convert_helper.class.php: call to base_converter->convert()
- line 421 of \backup\controller\restore_controller.class.php: call to convert_helper::to_moodle2_format()
- line 35 of \backup\restore.php: call to restore_controller->convert()