Hi, I have a strange exception at my class destructor: First-chance exception reading location 0x00000

class DispLst{
  // For fast instance existance test
  std::set< std::string > instances;
  [...]



DispLst::~DispLst(){
  this->clean();
  DeleteCriticalSection( &instancesGuard );
} <---- here instances destructor raises exception

Call stack:

X.exe!std::_Tree,std::allocator >,std::less,std::allocator > >,std::allocator,std::allocator > >,0> >::begin() Line 556 + 0xc bytes C++

X.exe!std::_Tree,std::allocator >,std::less,std::allocator > >,std::allocator,std::allocator > >,0> >::_Tidy() Line 1421 + 0x64 bytes C++

X.exe!std::_Tree,std::allocator >,std::less,std::allocator > >,std::allocator,std::allocator > >,0> >::~_Tree,std::allocator >,std::less,std::allocator > >,std::allocator,std::allocator > >,0> >() Line 541 C++

X.exe!std::set,std::allocator >,std::less,std::allocator > >,std::allocator,std::allocator > > >::~set,std::allocator >,std::less,std::allocator > >,std::allocator,std::allocator > > >() + 0x2b bytes C++

X.exe!DispLst::~DispLst() Line 82 + 0xf bytes C++

The exact place of error in xtree:

void _Tidy()
{   // free all storage
    erase(begin(), end());  <-------------------  HERE
    this->_Alptr.destroy(&_Left(_Myhead));
    this->_Alptr.destroy(&_Parent(_Myhead));
    this->_Alptr.destroy(&_Right(_Myhead));
    this->_Alnod.deallocate(_Myhead, 1);
    _Myhead = 0, _Mysize = 0;
}

iterator begin()
{   // return iterator for beginning of mutable sequence
    return (_TREE_ITERATOR(_Lmost())); <---------------- HERE
}

What is going on ? I'm using Visual Studio 2008.