Well, it depends on the PHP version you are using. I have worked lately to fix some php 8 compatibility, but still have to find the time to complete it and publish it. Please also note that OpenUpload is old. You might find a better solution out in the internet.
Well 500 means internal error. It's something related to configuration, but you need to look at the web server logs.
Well, openupload is quite OLD, so I'd try use something else.
It's a utf8 / iso conversion problem. You should put the Html code for special characters to avoid it. https://www.rapidtables.com/web/html/html-codes.html
Registration form not working
I've uploaded a new version with the fix. 0.4.4
Never mind I found the error. ereg_replace was removed from php 7. It must be replaced with preg_replace. File is lib/modules/default/auth.inc.php line 131
Can you check the web server logs for any hint on what the error is? Also what version of PHP are you using?