c# - Adding Class Library Reference to WCF Service Library -

i'm working on first web service, , i'm having trouble referencing class library have in solution inside of web service. here service:

using mydomain;  namespace webservices {     public class automatedlogin : iautomatedlogin     {         public guid gettoken(string email)         {             //code goes here         }     } } 

when add reference mydomain inside wcf service library, intellisense recognizes reference, when rebuild solution, compiler throws following error:

the type or namespace name 'mydomain' not found (are missing using directive or assembly reference?)

can tell me why compiler ignoring mydomain reference when try rebuild solution?

i able find similar question: wcf service library project can't find reference other project

i changed project's target framework .net framework 4 client profile .net framework 4 seems have fixed compiling issue.