C++ Builder XE2에 xstring에서 다음과 같은 에러가 뜹니다.

[BCC32 Error] xstring(530): E2031 Cannot cast from 'UnicodeString &' to 'char'

  Full parser context

    xstring(522): decision to instantiate: void void string::_Construct<_Vector_iterator<UnicodeString,allocator<UnicodeString> > >(_Vector_iterator<UnicodeString,allocator<UnicodeString> >,_Vector_iterator<UnicodeString,allocator<UnicodeString> >,forward_iterator_tag)

    --- Resetting parser context for instantiation...

    Unit14.cpp(6): #include Unit14.h

    Unit14.h(10): #include DShowSupporter.h

    DShowSupporter.h(6): #include C:\Program Files (x86)\Embarcadero\RAD Studio\9.0\include\boost_1_39\boost\tr1\tr1\vector

    vector(20): #include c:\program files (x86)\embarcadero\rad studio\9.0\include\../include/dinkumware/vector

    vector(6): #include C:\Program Files (x86)\Embarcadero\RAD Studio\9.0\include\boost_1_39\boost\tr1\tr1\stdexcept

    stdexcept(23): #include c:\program files (x86)\embarcadero\rad studio\9.0\include\../include/dinkumware/stdexcept

    stdexcept(6): #include c:\program files (x86)\embarcadero\rad studio\9.0\include\dinkumware\xstring

    xstring(6): namespace std

    xstring(357): class basic_string<_Elem,_Traits,_Ax>

    xstring(522): parsing: void void string::_Construct<_Vector_iterator<UnicodeString,allocator<UnicodeString> > >(_Vector_iterator<UnicodeString,allocator<UnicodeString> >,_Vector_iterator<UnicodeString,allocator<UnicodeString> >,forward_iterator_tag)

실제 xstring에서 에러가 난 코드는 

append((size_type)1, (_Elem)*_First);

이고요 

Main 코드에서

vector<String> mDeviceList;

string s_mDeviceList(mDeviceList.begin(), mDeviceList.end());

이 코드를 주석을 달면 에러가 사라지내요

뭔가 인터넷에서본 Vector를 string형으로 바꾸는걸 잘못 이해한것같은대 조언해 주시면 감사하겠습니다.