Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineWindow.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineWindow.cpp	(revision 74878)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/UIMachineWindow.cpp	(revision 74879)
@@ -138,5 +138,5 @@
     /* Check if we want Window Manager to distinguish Virtual Machine windows: */
     if (gEDataManager->distinguishMachineWindowGroups(vboxGlobal().managedVMUuid()))
-        strWindowName = QString("VirtualBox Machine UUID: %1").arg(vboxGlobal().managedVMUuid());
+        strWindowName = QString("VirtualBox Machine UUID: %1").arg(vboxGlobal().managedVMUuid().toString());
     /* Assign WM_CLASS property: */
     VBoxGlobal::setWMClass(this, strWindowName, strWindowClass);