在wcf中返回数据时出错？

Question

执行错误消息的GetAll_SamplePriscriptionDrug函数时

public EpriscriptionSrv()
{
using (var ctx = new EpriscriptionContext())
{
ctx.Configuration.ProxyCreationEnabled = false;
LstSamplePriscriptionDrug = ctx.SamplePriscriptionDrug.ToList();
}           
}

public static List<SamplePriscriptionDrug> LstSamplePriscriptionDrug = new List<SamplePriscriptionDrug>();


[OperationContract]
public List<SamplePriscriptionDrug> GetAll_SamplePriscriptionDrug()
{
    return LstSamplePriscriptionDrug;
}