fixed checker and added a test case

src/compiler/checker.ts

@@ -3508,7 +3508,16 @@ module ts {
                 }
                 if (reportErrors) {
                     headMessage = headMessage || Diagnostics.Type_0_is_not_assignable_to_type_1;
-                    reportError(headMessage, typeToString(source), typeToString(target));
+                    var sourceType = typeToString(source);
+                    var targetType = typeToString(target);
+                    if (sourceType !== targetType) {
+                        reportError(headMessage, sourceType, targetType);
+                    } else {
+                        // If the types are incompatible but have the same name, use the qualified names to give
+                        // a more insightful error message
+                        reportError(headMessage, getFullyQualifiedName(source.symbol), getFullyQualifiedName(target.symbol));
+                    }
+                    //reportError(headMessage, typeToString(source), typeToString(target));
                 }
                 return Ternary.False;
             }

tests/cases/compiler/differentTypesWithSameName.ts

@@ -0,0 +1,16 @@
+module m {
+  export class variable{
+    s: string;
+  }
+  export function doSomething(v: m.variable) {
+    
+  }
+}
+
+class variable {
+ t: number;
+}
+
+
+var v: variable = new variable();
+m.doSomething(v);