怎样在ole db中执行参数查询？

我不想用向导生成的访问器，为什么下面的代码不可行(编译通过，执行出错)？

::CoInitialize(NULL);

CDataSource ds;
CSession ss;
HRESULT hr;

ds.OpenFromInitializationString(L"Provider=SQLOLEDB;Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=pubs;Data Source=TIMDONG;Use Procedure for Prepare=1;Auto Translate=True;Packet Size=4096;Workstation ID=TIMDONG;Use Encryption for Data=False;Tag with column collation when possible=False");

ss.Open(ds);

CCommand<CDynamicParameterAccessor> cmd;
hr = cmd.Create(ss, "SELECT * FROM authors WHERE au_lname = '?'");

char* pParam = new char[6];
strcpy(pParam, "Green");
cmd.SetParamString(1, pParam);
cmd.Open(); // <----Error!!!

delete[] pParam;

cmd.Close();
ss.Close();
ds.Close();

::CoUninitialize();