The example program below will exhibit the problem when compiled with -std=c++0x or gnu++0x flag. The fix appears to be trivial, but requires a change to <ext/algorithm> header.

Example program:
#include <iostream>
#include <ext/rope>

using namespace std;

int main(int argc, char **argv)
{
	__gnu_cxx::crope line("test-test-test");

	cout << line.c_str() << endl;
	return 0;
}

Compilation error message:
In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/ropeimpl.h:48,                                                                  
                 from /usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/rope:2956,                                                                      
                 from testrope.cpp:2:                                           
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/algorithm: In function &#8216;std::pair<_InputIter, _ForwardIter> __gnu_cxx::copy_n(_InputIterator, _Size, _OutputIterator) [with _InputIterator = char*, _Size = long unsigned int, _OutputIterator = char*]&#8217;:                                                             
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/ropeimpl.h:1090:   instantiated from &#8216;static _CharT* __gnu_cxx::rope<_CharT, _Alloc>::_S_flatten(__gnu_cxx::_Rope_RopeRep<_CharT, _Alloc>*, _CharT*) [with _CharT = char, _Alloc = std::allocator<char>]&#8217;
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/ropeimpl.h:1621:   instantiated from &#8216;const _CharT* __gnu_cxx::rope<_CharT, _Alloc>::c_str() const [with _CharT = char, _Alloc = std::allocator<char>]&#8217;
testrope.cpp:10:   instantiated from here
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/algorithm:127: error: call of overloaded &#8216;__copy_n(char*&, long unsigned int&, char*&, std::random_access_iterator_tag)&#8217; is ambiguous
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/algorithm:78: note: candidates are: std::pair<_InputIter, _ForwardIter> __gnu_cxx::__copy_n(_InputIterator, _Size, _OutputIterator, std::input_iterator_tag) [with _InputIterator = char*, _Size = long unsigned int, _OutputIterator = char*]
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/ext/algorithm:93: note:                 std::pair<_InputIter, _ForwardIter> __gnu_cxx::__copy_n(_RAIterator, _Size, _OutputIterator, std::random_access_iterator_tag) [with _RAIterator = char*, _Size = long unsigned int, _OutputIterator = char*]
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/bits/stl_algo.h:1003: note:                 _OutputIterator std::__copy_n(_RandomAccessIterator, _Size, _OutputIterator, std::random_access_iterator_tag) [with _RandomAccessIterator = char*, _Size = long unsigned int, _OutputIterator = char*]
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.2/include/g++-v4/bits/stl_algo.h:988: note:                 _OutputIterator std::__copy_n(_InputIterator, _Size, _OutputIterator, std::input_iterator_tag) [with _InputIterator = char*, _Size = long unsigned int, _OutputIterator = char*]