Error:
There was a problem completing activation of the JW Player Plugin for WordPress. Please note that the JWPlayer Plugin for WordPress requires that the WordPress uploads directory exists and is writable. For tips on how to make sure this folder is writable please refer to Changing File Permissions WordPress Codex.
This may happen if you have moved your blog to another location/server.

Things to check.

Upload dir is chmod'ed to 777, also chmod the other year folders to 777.

chmod the following to 755

wp-content/uploads/jw-player-plugin-for-wordpress
wp-content/uploads/jw-player-plugin-for-wordpress/player
wp-content/uploads/jw-player-plugin-for-wordpress/configs

You should be good from there.