@[deleted], you have reported issues with the Standalone installer.
I also got the same report from Frederik, another user interested in OpenPetra.
Here is the error for everyone:
The message box says: "Login failed", "An error occured while trying to connect to the OpenPetra server! For details see the log file: C:\users\<username>\AppData\Roaming\OpenPetra\log30\PetraClient.log"
Frederic gave me that log file, and it complains about not being able to find the file
Exception occured: System.TypeInitializationException: Der Typeninitialisierer für "Sodium.SodiumCore" hat eine Ausnahme verursacht. ---> System.DllNotFoundException: Die DLL "libsodium.dll": Das angegebene Modul wurde nicht gefunden.
I thought I found the solution here: https://github.com/adamcaudill/libsodium-net/issues/111#issuecomment-158791421
But that did not solve the issue on the test laptop either.
So I guess the next step is to drop the use of libsodium from the Standalone OpenPetra. It is intended for demo usage anyway. For production I recommend to use Linux for the server and Windows for the client.
If you just want to try out OpenPetra, download the Windows client at https://demo.openpetra.org and play with some non-real data!