fstream::open问题

我写了下面的代码：
std::fstream Pointfile;
Pointfile.open(_panel->GetPath(),std::fstream::in);
出现的问题：
d:\myproject\caacreatecruve\caacreatecruve.m\src\caacreatepointcmd.cpp(277) : error C2668: 'std::basic_fstream<_Elem,_Traits>:pen' : ambiguous call to overloaded function
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        c:\program files\microsoft visual studio 8\vc\include\fstream(912): could be 'void std::basic_fstream<_Elem,_Traits>:pen(const char *,std::ios_base:penmode,int)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        c:\program files\microsoft visual studio 8\vc\include\fstream(870): or 'void std::basic_fstream<_Elem,_Traits>:pen(const wchar_t *,std::ios_base:penmode,int)'
        with
        [
            _Elem=char,
            _Traits=std::char_traits<char>
        ]
        while trying to match the argument list '(CATUnicodeString, const std::_Iosb<_Dummy>::_Openmode)'
        with
        [
            _Dummy=int
        ]
请问该怎么解决啊？