Boost shared_ptr无法强制转换为模板化基础

Question

问题是我为什么会收到以下错误以及如何修复错误：

error C2664: 'work<T>::setPrev' : cannot convert parameter 1 from 'boost::shared_ptr<T>' to 'boost::shared_ptr<T>'

cCapital类中对函数setPrev的调用给出了错误。

template <class T> class work
{
    public:
        work(const T & value):m_prev(), m_data(value) {}
        ~work(){}

        boost::shared_ptr<work> getPrev() const {return m_prev;}
        const T & value() const {return data;}
        void setPrev(boost::shared_ptr<work> elem) {m_prev = elem;}
        void setValue(const T & value) {data = value;}

    private:
        boost::shared_ptr<work> m_prev;
        T m_data;
};

class cAssetBase
{
    public:
        cAssetBase(const std::string & desc):m_desc(desc){}
        ~cAssetBase(){}
        const std::string & getDesc() const
        {
            return m_desc;
        }
    private:
        std::string m_desc;
};  

class cAsset: public work<cAssetBase>
{
    public:
        cAsset(const int & id, const std::string & symbol):m_id(id),work(cAssetBase(symbol)){}
        ~cAsset(){}
    protected:
        int m_id;
};

class cCapitalBase
{
    public:
        cCapitalBase(const std::string & desc):m_desc(desc){}
        ~cCapitalBase(){}
        const std::string & getDesc() const
        {
            return m_desc;
        }
    private:
        std::string m_desc;
};  

class cCapital: public work<cCapitalBase>
{
    public:
        cCapital(const int & id, const std::string & symbol, boost::shared_ptr<cAsset> & asset):m_id(id),work(cCapitalBase(symbol)),m_asset(asset)
        {
            setPrev(m_asset);
        }
        ~cCapital(){}
    protected:
        int m_id;
        boost::shared_ptr<cAsset>  m_asset;
};