[ADO] How to retrieve adLongVarChar typed filed of recordset?

<In Visual C++ & ADO>
I tried to retrieve a field which its Type property is "adLongVarChar" and SQL-DB datatype is "TEXT".

field = fields->GetItem(0L);
if(field->Type == adLongVarChar) {
_bstr_t str = _bstr_t(field->Value);
}

Above code have raied an error.
The error is "Visual C++ Run Time Error"
Why does it occur?

Thanks

A programmer who loves Goethe.