diff --git a/core/DataTable/Renderer.php b/core/DataTable/Renderer.php
index 6fd073d5fbd751e48a7f6d3093fdadf0aa71b909..84efd8c935b45e3068ad8782f199adefeb5b0850 100644
--- a/core/DataTable/Renderer.php
+++ b/core/DataTable/Renderer.php
@@ -117,7 +117,7 @@ abstract class Piwik_DataTable_Renderer
 		$className = 'Piwik_DataTable_Renderer_' . $name;
 		
 		try {
-			Piwik_Loader::autoload($className);
+			Piwik_Loader::loadClass($className);
 			return new $className;			
 		} catch(Exception $e) {
 			$availableRenderers = implode(', ', self::getRenderers());
@@ -135,4 +135,4 @@ abstract class Piwik_DataTable_Renderer
 	{
 		return htmlentities($rawData, ENT_COMPAT, "UTF-8");
 	}
-}
\ No newline at end of file
+}
diff --git a/core/Loader.php b/core/Loader.php
index bb4a04be35e972171fc52e631ea3017033f41cf5..b6d24e2b7bb26818f44333ac1830cc2c0aa906de 100644
--- a/core/Loader.php
+++ b/core/Loader.php
@@ -47,8 +47,9 @@ class Piwik_Loader
 	 * Load class by name
 	 *
 	 * @param string $class Class name
+	 * @throws Exception if class not found
 	 */
-	public static function autoload($class)
+	public static function loadClass($class)
 	{
 		$classPath = self::getClassFileName($class);
 		while(!empty($classPath))
@@ -71,6 +72,20 @@ class Piwik_Loader
 			$lastSlash = strrpos($classPath, '/');
 			$classPath = ($lastSlash === false) ? '' : substr($classPath, 0, $lastSlash);
 		}
+		throw new Exception("Class \"$class\" not found.");
+	}
+
+	/**
+	 * Autoloader
+	 *
+	 * @param string $class Class name
+	 */
+	public static function autoload($class)
+	{
+		try {
+			@self::loadClass($class);
+		} catch (Exception $e) {
+		}
 	}
 }
 
diff --git a/core/Session.php b/core/Session.php
index 49969f2066113cd7722e16c46e6c885dccd1318c..490e1b2ce57d8e253412262fef144d9180c37500 100644
--- a/core/Session.php
+++ b/core/Session.php
@@ -67,6 +67,11 @@ class Piwik_Session extends Zend_Session
 			}
 		}
 
-		Zend_Session::start();
+		try {
+			Zend_Session::start();
+		} catch(Exception $e) {
+			// This message is not translateable because translations haven't been loaded yet.
+			Piwik_ExitWithMessage('Unable to start session.  Check that session.save_path or tmp/sessions is writeable.');
+		}
 	}
 }