The upload error message can also be displayed when the actual settings of the import dialog are suppressing an import.
Take the error messages with a grain of salt. File permisson problem is most common, but not with a 100% guess rate.
Try Filter blank email addresses/Filter duplicate records on off.
Add a few dummy tokens and export the token file and try to reimport it.What is the result?
To tackle the issue of permissions you have to know what is the default settings of the software stack you're using (e.g. Apache+PHP) and how you transfer files (FTP-User).
To modify the PHP-Code isn't sustainable for most users since they have to modify the code with every update of LimeSurvey or just back away from updating Limesurvey at all.
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