Index: /trunk/src/VBox/Main/ProgressImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/ProgressImpl.cpp	(revision 29923)
+++ /trunk/src/VBox/Main/ProgressImpl.cpp	(revision 29924)
@@ -1009,5 +1009,7 @@
     AutoWriteLock alock(this COMMA_LOCKVAL_SRC_POS);
 
-    AssertReturn(!mCompleted && !mCanceled, E_FAIL);
+    if (mCanceled)
+        return E_FAIL;
+    AssertReturn(!mCompleted, E_FAIL);
     AssertReturn(m_ulCurrentOperation + 1 < m_cOperations, E_FAIL);