Index: plugins.php
===================================================================
--- plugins.php	(revision 6603)
+++ plugins.php	(working copy)
@@ -4,7 +4,7 @@
 if ( isset($_GET['action']) ) {
 	if ( 'activate' == $_GET['action'] ) {
 		check_admin_referer('activate-plugin_' . $_GET['plugin']);
-		$result = activate_plugin($_GET['plugin'], 'plugins.php?error=true&plugin=' . $plugin);
+		$result = activate_plugin($_GET['plugin'], 'plugins.php?error=true&plugin=' . $_GET['plugin']);
 		if ( is_wp_error( $result ) )
 			wp_die( $result->get_error_message() );
 		wp_redirect('plugins.php?activate=true'); // overrides the ?error=true one above