Do you see anything in the Wowza logs which may indicate what the issue is?
You're getting the sign in page when entering the following URL in the browser but the username/password doesn't work when you click the Sign In button?
Ensure you have a username and password in the [Wowza-Install]/conf/admin.password file.
If you're still unable to get this working, please can you open a ticket by sending an email to firstname.lastname@example.org.
More information on getting started can be found in the Quick Start Guide.