I just had a very strange problem where my WordPress Admin was unable to connect to the WordPress.org Plugin Repository.
The popular-tags cloud failed to load, and instead displayed this error:
An unexpected error occurred. Something may be wrong with WordPress.org or this server's configuration…
And if i tried to search for a plugin, the entire page went grey and displayed the same error message.
The solution was to have my hosting provider (HostGator) "restart my name-server cache" for my server. That fixed the problem for me.