Installing Different Themes

I recently downloaded a WordPress theme from Themeforest. Everything went ok with the download and everything but I can’t seem to upload the theme. I am trying to install the theme onto an ‘Add On’ domain and when I click on ‘Add New’ theme, this message comes up: “An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums”. I can still find the .zip file I need and it seems to be loading but once it finishes an error screen comes up saying that the install failed. I’m at a loss… Any and all help would be appreciated.. Thanks in advance.

P.S. That message also comes up when i try to upload a theme onto a different “Add On’ domain that i have in my hosting account.