diff --git a/Mesh_3/demo/Mesh_3/CMakeLists.txt b/Mesh_3/demo/Mesh_3/CMakeLists.txt
index ddd4579827b..9fd12c0add4 100644
--- a/Mesh_3/demo/Mesh_3/CMakeLists.txt
+++ b/Mesh_3/demo/Mesh_3/CMakeLists.txt
@@ -215,8 +215,7 @@ if(CGAL_Qt4_FOUND AND QT4_FOUND AND OPENGL_FOUND AND QGLVIEWER_FOUND)
   polyhedron_demo_plugin(io_c3t3_plugin Io_c3t3_plugin)
   target_link_libraries(io_c3t3_plugin scene_c3t3_item)
 
-  file ( GLOB RIBPLUGIN_EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/c3t3_rib_exporter_plugin.cpp" )
-  if ( RIBPLUGIN_EXISTS )
+  if ( EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/c3t3_rib_exporter_plugin.cpp" )
     polyhedron_demo_plugin(c3t3_rib_exporter_plugin C3t3_rib_exporter_plugin ${ribUI_FILES})
     target_link_libraries(c3t3_rib_exporter_plugin scene_c3t3_item viewer)
   endif()
diff --git a/Mesh_3/demo/Mesh_3/Mesh_3_optimization_plugin.cpp b/Mesh_3/demo/Mesh_3/Mesh_3_optimization_plugin.cpp
index b0030ae7bb0..3d2fd0c76cf 100644
--- a/Mesh_3/demo/Mesh_3/Mesh_3_optimization_plugin.cpp
+++ b/Mesh_3/demo/Mesh_3/Mesh_3_optimization_plugin.cpp
@@ -421,7 +421,7 @@ get_c3t3_item() const
   
   if ( NULL == item )
   {
-    QMessageBox::critical(mw,tr(""),
+    QMessageBox::warning(mw,tr(""),
                           tr("Selected object is not a mesh... optimization can't be performed"));
     return NULL;
   }
diff --git a/Mesh_3/demo/Mesh_3/Mesh_3_plugin.cpp b/Mesh_3/demo/Mesh_3/Mesh_3_plugin.cpp
index ae92f46b3ce..d9169a0c234 100644
--- a/Mesh_3/demo/Mesh_3/Mesh_3_plugin.cpp
+++ b/Mesh_3/demo/Mesh_3/Mesh_3_plugin.cpp
@@ -136,7 +136,7 @@ void Mesh_3_plugin::mesh_3()
 
   if ( NULL == item )
   {
-    QMessageBox::critical(mw,tr(""),
+    QMessageBox::warning(mw,tr(""),
                           tr("Selected object can't be meshed")); 
     return;
   }