CPtrList的AddTail方法出错，郁闷郁闷郁闷郁闷

void CDataProcess::InitNewTrain(CString temp, int id)

{

	static int num=0;

	CTrain *ptrain=new CTrain(this,temp,id);

	num++;

	



	_CommandPtr pCommand;

	pCommand.CreateInstance("ADODB.Command");

	try

	{

		pCommand->ActiveConnection = theApp.m_pConnection_statistics;

	}

	catch (_com_error* e)

	{

		AfxMessageBox(e->ErrorMessage());

	}

	CString cmdstr;



	cmdstr.Format("Insert into TrainInfo values (%d,'%s','%s','%s','%s')",num,ptrain->m_TrainParam.strTrainID,ptrain->m_TrainParam.strTrainType,ptrain->m_TrainParam.strTrainLong,ptrain->m_TrainParam.strTrainWeight);

	pCommand->CommandText = _bstr_t(cmdstr);

	pCommand->Execute(NULL, NULL, adCmdText);



	cmdstr.Format("Insert into TrainInfo values (%d,'%s','%s','%s','%s')",num,ptrain->m_TrainParam.strTrainID,ptrain->m_TrainParam.strTrainType,ptrain->m_TrainParam.strTrainLong,ptrain->m_TrainParam.strTrainWeight);

	pCommand->CommandText = _bstr_t(cmdstr);

	pCommand->Execute(NULL, NULL, adCmdText);





	CClientDC dc(m_pParentWnd);

	((CCTCSFaceView* )m_pParentWnd)->OnPrepareDC(&dc);



	ptrain->DrawTrain(&dc);

	m_Trainlist.AddTail(ptrain);//  m_Trainlist 是一个CPtrList类型的类成员变量

}

出错行是AddTail那句。
弹出Debug Assertion Failed！
File：list_p.cpp
Line:151
然后我跟踪到提示错误的文件的哪一行
POSITION CPtrList::AddHead(void* newElement)
{

ASSERT_VALID(this);

CNode* pNewNode = NewNode(NULL, m_pNodeHead);
pNewNode->data = newElement;
if (m_pNodeHead != NULL)
m_pNodeHead->pPrev = pNewNode;
else
m_pNodeTail = pNewNode;
m_pNodeHead = pNewNode;
return (POSITION) pNewNode;

}
指向这个函数的ASSERT_VALID(this);这一行


如此简单的操作会有这样的错误呢？？？？

PS：我后来测试发现：在出错函数中定义一个CPtrList变量然后执行AddTail是可以的，就是不能使用定义的成员变量，真是搞不懂了，郁闷郁闷郁闷郁闷郁闷！！！！！！！！！