As others have posted, it’s currently not updating to the latest 3.7 Beta.

I’m running 3.6.1. The following image shows the results of the update page along with my current Beta Test plugin settings.

http://cl.ly/image/1q470I0k0F0l

Also, on a side note, now that development is occurring on both 3.7 and 3.8 simultaneously, it would be good to see an option that allows you to select which of these versions you want to install.

http://wordpress.org/plugins/wordpress-beta-tester/