Hi Martin,
OutSystems is a Platform for developing web applications. So it could very well be the job application form is created by using OutSystems. Unfortunately, though OutSystems is a great tool, it's possible to create bugs with it as well. A 500 error means "internal server error", which could mean that the connection between the Outsystems front end and the company's back end is broken. On the other hand, you are saying that the application says the password is invalid, which doesn't sound as an HTML 500 error?
Anyway, unfortunately, there's nothing that we (the Community) can do anything about. So my suggestion would be to show the company the error, and tell them it's not possible for you to fill out the form, and ask them if there's another way to submit your application (and perhaps suggest they have their software department check the error!).