diff --git a/app/models/submission.rb b/app/models/submission.rb
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -34,8 +34,8 @@
 
   def self.find_in_range_by_user_and_problem(user_id, problem_id,since_id,until_id)
     records = Submission.where(problem_id: problem_id,user_id: user_id)
-    records = records.where('id >= ?',since_id) if since_id > 0
-    records = records.where('id <= ?',until_id) if until_id > 0
+    records = records.where('id >= ?',since_id) if since_id and since_id > 0
+    records = records.where('id <= ?',until_id) if until_id and until_id > 0
     records.all
   end
 
@@ -137,7 +137,7 @@
 
     # for output_only tasks
     return if self.problem!=nil and self.problem.output_only
-    
+
     if self.language==nil
       errors.add('source',"Cannot detect language. Did you submit a correct source file?") unless self.language!=nil
     end
@@ -147,8 +147,12 @@
     return if self.source==nil
     if self.problem==nil
       errors.add('problem',"must be specified.")
-    elsif (!self.problem.available) and (self.new_record?)
-      errors.add('problem',"must be valid.")
+    else
+      #admin always have right
+      return if self.user.admin?
+
+      #check if user has the right to submit the problem
+      errors.add('problem',"must be valid.") if (!self.user.available_problems.include?(self.problem)) and (self.new_record?)
     end
   end