It looks like you are using the wrong class path for ModuleRTMPAuthenticate, for Wowza 3.5 and up the class path should be:
This is probably not the issue, but will clean up the logs and fix the error as well as enabling the module.
Also, if you are not using Smooth Streaming you should disable it any other LiveStreamPacketizers you are not using.
Do you have any custom modules enabled in the application?
What is the load like on the server?
What type of streaming are you doing and what is the source?
Once you have made the recommended changes, please restart Wowza in stand-alone mode [install-dir]/bin/startup.bat and post the start up messages from the console so we can take a look.