more precise error message for start date scheduling violation

app/models/work_package/validations.rb

@@ -95,7 +95,9 @@ module WorkPackage::Validations
 
   def validate_start_date_before_soonest_start_date
     if start_date && soonest_start && start_date < soonest_start
-      errors.add :start_date, :invalid
+      errors.add :start_date,
+                 :violates_relationships,
+                 soonest_start: soonest_start
     end
   end
 

config/locales/en.yml

@@ -409,6 +409,8 @@ en:
               cannot_be_in_another_project: "cannot be in another project."
               not_a_valid_parent: "is invalid."
               does_not_exist: "does not exist."
+            start_date:
+              violates_relationships: "can only be set to %{soonest_start} or later so as not to violate the work package's relationships."
             status_id:
               status_transition_invalid: "is invalid because no valid transition exists from old to new status for the current user's roles."
             priority_id: