Q:

Can't insert or delete records in SQL Server 2014 using Visual Studio 2013

Context
I am using Visual Studio 2013, and I have created an ADO.Net Entity Data Model which connect to my SQL Server 2014 database.
I can retrieve my data and display it using RESTful services.
Problem
But I can't insert a data into any table (delete and edit too). 
Is my connection set to read-only mode? I looked to the properties of my DB but nothing points to that option. 
Any help?!
Edited: 
Here is my code of WCF Service. Below is Create() body:
using (OnlinestoreEntities ose = new OnlinestoreEntities())
{
    try
    {
        UserEntity user = new UserEntity();
        user.Id = _user.Id;
        user.Name = _user.Name;
        user.Password = _user.Password;
        user.Email = _user.Email;

        ose.UserEntities.Add(user);
        ose.SaveChanges();

        return true;
    }
    catch
    {
        return false;
    }
};

The following code is Create() on the client side (using MVS model), this function is called from the controller when clicks in the Add User link:
public bool Create(User user)
{
    try
    {
        var webClient = new WebClient();
        DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(User));

        MemoryStream mem = new MemoryStream();
        ser.WriteObject(mem, user);

        string data = Encoding.UTF8.GetString(mem.ToArray(), 0, (int)mem.Length);

        webClient.Headers["Content-type"] = "application/json";
        webClient.Encoding = Encoding.UTF8;

        String str = webClient.UploadString(BASE_URL + "create", "POST", data);
        return true;
    }
    catch
    {
        return false;
    }
}

Do you still need any details, I thought the problem was about DB settings?!

A:

Look like the username you are using to connect the SQL database have read only access. You should use some other username which have permission to do DML operation.
In case you not have another username then you have to contact the DBA for your  SQL server
EDIT
When installing SQL server you will get option to configure, how your authenticate SQL Server (i.e. Windows Authentication mode or Mixed Mode). I'll prefer mixed mode.
Then after selecting mixed mode you have to configur your 'SA' password. 
To me its look like you are using windows authentication, and only you have admin access and Everyone else configure as readonly.
When you deploy ASP.Net application in IIS. By default It take the AppPoolIdentity to open SQL connection, which not have any permission to do DML operation

