Also experiencing this problem, although SKU does not seem to be the cause (our SKUS is in the format "FOO - ####"), so none of them contain about 64 characters.
When I select the csv file and select the check data, it passes the verification penalty:
Checked rows: 1718, checked entities: 47, invalid rows: 0, total errors: 0
File is valid! To start import process press "Import" button
After choosing the import, I get this error:
SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`magentoss`.`catalog_product_option_type_value`, CONSTRAINT `FK_CAT_PRD_OPT_TYPE_VAL_OPT_ID_CAT_PRD_OPT_OPT_ID` FOREIGN KEY (`option_id`) REFERENCES `catalog_product_option` (`option_id`) ON D), query was: INSERT INTO `catalog_product_option_type_value` (`option_type_id`,`sort_order`,`sku`,`option_id`) VALUES (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?), (?, ?, ?, ?)
After checking the product lists, it seems that the file has been downloaded, since all my data has been updated, so I’m not quite sure what is happening.