A linking error I don't understand

["Incongruous ..." <incongruous outlook com>]

I am using Visual Studio 2010 32bit to compile a program using gtkmm32 and in VS2012 I am using gtkmm64, I have no problem compiling and running under 32 bit, but in the 64 bit I get this linking error:
 
1>contactframe.obj : error LNK2019: unresolved external symbol
"__declspec(dllimport) protected:
class std::_List_iterator<class std::_List_val<struct std::_List_simple_types
<class sigc::slot_base> > > __cdecl sigc::signal_base::connect(
class sigc::slot_base const &)"
(__imp_?connect signal_base@sigc@@IEAA?AV?$_List_iterator V?$_List_val@U?
$_List_simple_types Vslot_base@sigc@@@std@@@std@@@std@@AEBVslot_base 2@@Z) referenced in function
 "public: struct sigc::slot_iterator<class sigc::slot
<void,struct sigc::nil,struct sigc::nil,struct sigc::nil,
struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil> >
 __cdecl sigc::signal0<void,struct sigc::nil>::connect(
class sigc::slot<void,struct sigc::nil,struct sigc::nil,
struct sigc::nil,struct sigc::nil,struct sigc::nil,struct
sigc::nil,struct sigc::nil> const &)"
(?connect ?$signal0@XUnil sigc@@@sigc@@QEAA?AU?$slot_iterator V?$slot@XUnil sigc@@U12 U12@U12 U12@U12 U12@@sigc@@@2 AEBV?$slot@XUnil sigc@@U12 U12@U12 U12@U12 U12@@2@@Z)
 
What am I doing wrong?