c# – WCF中的远程主机强制关闭现有连接

[DataContract]
public abstract class Template
{
    [DataMember]
    public virtual int? Id { get; set; }
    [DataMember]
    public virtual string Title { get; set; }
    [DataMember]
    public virtual byte[] TemplateDoc { get; set; }
    [DataMember]
    public virtual bool IsSystemTemplate { get; set; }        
}

两个派生类：UserTemplate和SystemTemplate实现上面的抽象类,定义如下：

public class UserTemplate : Template
{
    [DataMember]
    public virtual Int32? OfficeId { get; set; }

    [DataMember]
    public virtual Int32? UserId { get; set; }

    protected UserTemplate() { }

    public UserTemplate(string title,byte[] templateDoc,string templateDocName,TemplateType templateType,int officeId,int? userId)
    {
        this.Title = title;
        this.TemplateDoc = templateDoc;
        this.IsSystemTemplate = false;
        this.OfficeId = officeId;
        this.UserId = userId;
    }
}

public class SystemTemplate : Template
{
    [DataMember]
    public virtual Int32? MultiListGroupId { get; set; }

    protected SystemTemplate() { }

    public SystemTemplate(string title,int multiListGroupId)
    {
        this.Title = title;
        this.TemplateDoc = templateDoc;
        this.IsSystemTemplate = true;
        this.MultiListGroupId = multiListGroupId;
    }
}

现在,当我尝试调用以下服务方法时：

List<Template> GetTemplatesByTemplateType(int officeId,int? userId,TemplateType templateType)

我收到此错误：

System.Net.sockets.socketException: An existing connection was forcibly closed by the remote host

是因为我试图返回抽象类的原因吗？
如果我尝试使用单元测试调用此方法,它运行正常.