Welcome to the ODK forum, @niyonsaba! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
If you're setting up a new server, I really suggest you take a look at ODK Central. Aggregate is no longer being updated. ODK Central is now the ODK server.
In order to troubleshoot your issue, are you able to upload your form file here? Can you add a screenshot of the error message?