diff --git a/IRaCIS.Core.Application/Service/Allocation/TaskConsistentRuleService.cs b/IRaCIS.Core.Application/Service/Allocation/TaskConsistentRuleService.cs
index cec701d73..82a04ee8a 100644
--- a/IRaCIS.Core.Application/Service/Allocation/TaskConsistentRuleService.cs
+++ b/IRaCIS.Core.Application/Service/Allocation/TaskConsistentRuleService.cs
@@ -156,7 +156,11 @@ namespace IRaCIS.Core.Application.Service
                     {
                         var maxCodeStr = _visitTaskRepository.Where(t => t.TrialId == subject.TrialId && t.TrialReadingCriterionId == trialReadingCriterionId).OrderByDescending(t => t.BlindSubjectCode).Select(t => t.BlindSubjectCode).FirstOrDefault();
 
-                        int.TryParse(maxCodeStr.Substring(maxCodeStr.Length - filterObj.BlindSubjectNumberOfPlaces), out maxCodeInt);
+                        if (maxCodeStr != String.Empty)
+                        {
+                            int.TryParse(maxCodeStr.Substring(maxCodeStr.Length - filterObj.BlindSubjectNumberOfPlaces), out maxCodeInt);
+
+                        }                      
 
                         blindSubjectCode = filterObj.BlindTrialSiteCode + (maxCodeInt + 1).ToString($"D{filterObj.BlindSubjectNumberOfPlaces}");
                     }