Index: src/lang/english.txt
===================================================================
--- src/lang/english.txt	(revisión: 27386)
+++ src/lang/english.txt	(copia de trabajo)
@@ -844,6 +844,7 @@
 STR_NEWS_VEHICLE_HAS_VOID_ORDER                                 :{WHITE}{VEHICLE} has a void order
 STR_NEWS_VEHICLE_HAS_DUPLICATE_ENTRY                            :{WHITE}{VEHICLE} has duplicate orders
 STR_NEWS_VEHICLE_HAS_INVALID_ENTRY                              :{WHITE}{VEHICLE} has an invalid station in its orders
+STR_NEWS_VEHICLE_HAS_INVALID_CONDITIONAL                        :{WHITE}{VEHICLE} has an invalid condition in its orders (less than 0)
 STR_NEWS_PLANE_USES_TOO_SHORT_RUNWAY                            :{WHITE}{VEHICLE} has in its orders an airport whose runway is too short
 
 STR_NEWS_VEHICLE_IS_GETTING_OLD                                 :{WHITE}{VEHICLE} is getting old
Index: src/order_cmd.cpp
===================================================================
--- src/order_cmd.cpp	(revisión: 27386)
+++ src/order_cmd.cpp	(copia de trabajo)
@@ -1800,6 +1800,14 @@
 					message = STR_NEWS_PLANE_USES_TOO_SHORT_RUNWAY;
 				}
 			}
+			/* Unfulfillable conditional orders */
+			if (order->IsType(OT_CONDITIONAL)) {
+				if ( (order->GetConditionComparator() == OCC_LESS_THAN) && (order->GetConditionValue() == 0) ) {
+					switch (order->GetConditionVariable()) {
+						case OCV_AGE: case OCV_LOAD_PERCENTAGE: case OCV_MAX_SPEED: case OCV_RELIABILITY: 
+							message = STR_NEWS_VEHICLE_HAS_INVALID_CONDITIONAL;
+						break;
+						default:
+						break;
+					}
+				}
+			}
 		}