c# - Entity Framework compilation error in return methods -

i imported database visual studio project. here code main.cs file:

using system; using system.collections.generic; using system.linq; using system.text; using system.threading.tasks;  namespace entityframework {     class program     {         static void main(string[] args)         {             northwindentities db = new northwindentities();              foreach (var customer in db.customers)             {                 console.writeline(customer.contactname);             }             db.dispose();         }     } } 

the problem error:

error cs1502: best overloaded method match 'system.data.entity.core.objects.objectcontext.executefunction(string, params system.data.entity.core.objects.objectparameter[])' has invalid arguments

when double click on automatically go method:

public virtual objectresult<custorderhist_result> custorderhist(string customerid)             {                 var customeridparameter = customerid != null ?                     new objectparameter("customerid", customerid) :                     new objectparameter("customerid", typeof(string));  //the error shows problem in return                 return ((iobjectcontextadapter)this).objectcontext.executefunction<custorderhist_result>("custorderhist", customeridparameter);             } 

it shows problem in return of method. error occurs everywhere return written. haven't written these functions. entity framework has created them automatically. have suggestions problem might be?

some ways investigate :

• are sure customerid in db in string format ? it
  not incremental int ?
• are using sql server or db ?

the autogenerated file.designer.cs ever simple stored procedure retrieve not complex object, think sp not correctly imported in edmx. check if sp method correct type i/o, check if using db sql server configure oledb.