Index: /trunk/src/org/openstreetmap/josm/actions/UploadAction.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/actions/UploadAction.java	(revision 1697)
+++ /trunk/src/org/openstreetmap/josm/actions/UploadAction.java	(revision 1698)
@@ -420,5 +420,5 @@
                         + "{0}"
                         + "</html>",
-                        e.getMessage()
+                        e.getMessage().replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
                 ),
                 tr("Precondition violation"),
@@ -461,5 +461,5 @@
                 + "{0}"
                 + "</html>",
-                e.getMessage()
+                e.getMessage().replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
         );
         JOptionPane.showMessageDialog(