I use the current version of Oracle SQL Developer, I started getting this error after the last update. I can not upload fixed length text fields anymore. I have to load it into Excel or LibreOffice and save it out as a .csv. Why can I not upload text files through developer anymore?
Please don't hijack another user's 4 year old thread for your own issues.
If you have a question or issue create a new thread and provide your specific information about the problem including the full version number for sql developer and the platform you are using.