Index: /trunk/src/org/openstreetmap/josm/data/validation/OsmValidator.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/validation/OsmValidator.java	(revision 11593)
+++ /trunk/src/org/openstreetmap/josm/data/validation/OsmValidator.java	(revision 11594)
@@ -4,4 +4,5 @@
 import static org.openstreetmap.josm.tools.I18n.tr;
 
+import java.awt.GraphicsEnvironment;
 import java.io.File;
 import java.io.FileNotFoundException;
@@ -334,9 +335,9 @@
             } catch (Exception e) {
                 Main.error(e);
-                JOptionPane.showMessageDialog(Main.parent,
-                        tr("Error initializing test {0}:\n {1}", test.getClass()
-                                .getSimpleName(), e),
-                                tr("Error"),
-                                JOptionPane.ERROR_MESSAGE);
+                if (!GraphicsEnvironment.isHeadless()) {
+                    JOptionPane.showMessageDialog(Main.parent,
+                            tr("Error initializing test {0}:\n {1}", test.getClass().getSimpleName(), e),
+                            tr("Error"), JOptionPane.ERROR_MESSAGE);
+                }
             }
         }