Hi Muhammed,
The error suggests that something is wrong with the csv file.
I suggest pinpointing the problem by checking the csv file first: what character is in line 342, positions 15, 165 and 483?
Could that character be a problem?
You may try removing line 342 and then retry to make sure this line is the only issue.
When i tried the uploader, i did run into issues with larger sheets with multiple tabs. After adding a 7th or 8th tab (not sure anymore) the import started to break and i had to split the sheet into multiple excels for it to work. So it could also be a bug in the excel importer. In that case Mendix should be able to help you when you create a support ticket.
I hope this helps.