--- wp-admin/includes/class-wp-upgrader.php	2013-12-14 17:02:47.573203177 +0000
+++ wp-admin/includes/class-wp-upgrader.php	2014-02-24 12:36:35.679401688 +0000
@@ -52,6 +52,7 @@
 		$this->strings['installing_package'] = __('Installing the latest version…');
 		$this->strings['no_files'] = __('The package contains no files.');
 		$this->strings['folder_exists'] = __('Destination folder already exists.');
+		$this->strings['remove_first'] = __('You cannot install over the top of an already existing entity - you need to de-install the existing version first.');
 		$this->strings['mkdir_failed'] = __('Could not create directory.');
 		$this->strings['incompatible_archive'] = __('The package could not be installed.');
 
@@ -364,6 +365,7 @@
 		$this->skin->set_result($result);
 		if ( is_wp_error($result) ) {
 			$this->skin->error($result);
+			if (@in_array('folder_exists', $result->get_error_codes())) $this->skin->feedback('remove_first');
 			$this->skin->feedback('process_failed');
 		} else {
 			//Install Succeeded