First of all I apologize, but we're during migration of our site and maybe there is still info that data import module is free. However we've developed this module from the scratch to add a lot of options so we've decided to charge some fee.
After registration you should write down your license key and if you wish to reinstall your EPESI, you can reuse your existing key and you'll be able to download your previously bought modules. But you can't use one key on simultanously running installations.
We haven't such issue and I suppose that you've got some server error that's not reported correctly to the browser.
Please enable REPORT_ALL_ERRORS (uncomment, change to '1') in data/config.php and open browser's console (F12) open EPESI, try to upload simple csv file and see if you'll get any error.