diff --git a/Lib/Exception/UsageException.php b/Lib/Exception/UsageException.php
new file mode 100644
index 0000000..af134e6
--- /dev/null
+++ b/Lib/Exception/UsageException.php
@@ -0,0 +1,5 @@
+<?php
+
+namespace BSR\Lib\Exception;
+
+class UsageException extends WebException {}
\ No newline at end of file
diff --git a/Lib/WebService.php b/Lib/WebService.php
index 97e2cf3..c70849b 100644
--- a/Lib/WebService.php
+++ b/Lib/WebService.php
@@ -2,8 +2,8 @@
 
 namespace BSR\Lib;
 
+use BSR\Lib\Exception\UsageException;
 use BSR\Lib\Exception\WebException;
-use BSR\Lib\Renderer;
 
 abstract class WebService
 {
@@ -74,18 +74,18 @@ abstract class WebService
 
         $params = empty($_GET) ? $_POST : $_GET;
         if (empty($params)) {
-            throw new WebException ("CallArgument", "arguments error", -1);
+            throw new UsageException("CallArgument", "arguments error", -1);
         }
 
         if (!array_key_exists("func", $params)) {
-            throw new WebException ("CallArgFunction", "no 'func' specified", -2);
+            throw new UsageException("CallArgFunction", "no 'func' specified", -2);
         }
 
         $this->func = $params["func"];
         unset($params['func']);
 
         if (!is_callable(array($this, $this->func))) {
-            throw new WebException ("CallFunction", "'func' method not available", -3);
+            throw new UsageException("CallFunction", "'func' method not available", -3);
         }
 
         $rm = new \ReflectionMethod($this, $this->func);
@@ -95,10 +95,10 @@ abstract class WebService
 
         /* Check the number of arguments. */
         if ($nbParams < $nbArgsFix) {
-            throw new WebException ("CallArgNumber", "you must provide at least " . $nbArgsFix . " arguments", 4);
+            throw new UsageException("CallArgNumber", "you must provide at least " . $nbArgsFix . " arguments", 4);
         }
         if ($nbParams > $nbArgs) {
-            throw new WebException ("CallArgNumber", "you must provide at most " . $nbArgs . " arguments", 4);
+            throw new UsageException("CallArgNumber", "you must provide at most " . $nbArgs . " arguments", 4);
         }
 
         $this->log("Calling '".$this->func."'");