[C++] Errore su struct "Type no matching function for call to..."

[Neptune]

Nel caso servisse l'intero codice lo trovate qui:
http://www.ideone.com/hmlQw

E l'errore che segnala ideone.com è questo:

prog.cpp: In member function ‘void hash_table<K, E>::insert(const mypair<const K, E>&) [with K = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, E = int]’:
prog.cpp:245:   instantiated from here
prog.cpp:222: error: no matching function for call to ‘mypair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>::mypair(const mypair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>&)’
prog.cpp:12: note: candidates are: mypair<K, E>::mypair(mypair<const K, E>&) [with K = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, E = int]
prog.cpp:11: note:                 mypair<K, E>::mypair() [with K = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, E = int]