Problems with registration process

Well, I hope that I finally found the right subforum... Okay, once again:

Hi..

First of all, I want to excuse for my bad English. English is not my mother tongue but I hope you understand me.

I use the Membership-Plugin 2.0.3 with the newest version of WordPress. I'm quite sure that I configured everything well. But the registration process doesn't work.

I log out of my admin account and try to register as a new member on this registration page:

http://www.knastinfo.de/mitglied-werden/anmeldung-einmonatskurs

I fill all required fields (username, email address, etc.) and click on "REGISTER MY ACCOUNT". But I don't get to the next page - the registration page simply reloads. I've tried out a lot of things in the last couple of hours - and still I cannot find the mistake.

Possibly some .php-files on my server do not have the right rights. Why do I think that? Well, I have exactly the same installation on an other server - and there it works fine.

Can you please tell me which files inside the membershipincludes-directory are responsible for the registration process? Would be helpful...

Any more suggestions? I appreciate any help! Thanks in advance.

Wittgen66