Had a security vulnerability on my server and after recovering my backup updated to version 2.0b3 by simply copying over to the target directory. Site is reachable and looks good - I can also login fine into admin. When I select the plugin manager though I get this:
This is how PHP expresses a closure. Which PHP version is used? Beta3 needs >= PHP 5.3.
Check (and update) your PHP version, anonymous functions are only supported on 5.3+.
For the bad case you can't, downgrade, or we will have to find a workaround for you. This is bad, but possible.