std::string operator == error！ help！

typedef std::vector<std::string> sTable;
sTable id_table;
.........
...........
sTable::iterator vi = id_table.begin();
bool intable = false;
int index = 0;

std::string tempstring = temp_string;

if(vi)
do{
if(*vi == tempstring){ // error！！
intable = true;
break;
}
index++;
}while(++vi);


error C2784: 'bool __cdecl std::operator ==(const class std::multimap<_K,_Ty,_
Pr,_A> &,const class std::multimap<_K,_Ty,_Pr,_A> &)' : could not deduce templ
ate argument for 'const class std::mu
ltimap<_K,_Ty,_Pr,_A> &' from 'class std::basic_string<char,struct std::char_t
raits<char>,class std::allocator<char> >'

可string 的opeartor == STL中重载过了啊，
怎么会类型不匹配啊？？
ft

ps：VC6。0下编译！