_debugger_hook_dummy = 0

Post the call stack that is dumped at the time of the crash.

Here it goes:

> msvcr90.dll!_crt_debugger_hook(int _Reserved=1220192) Line 65 C
msvcr90.dll!_invalid_parameter(const wchar_t * pszExpression=0x00000000, const wchar_t * pszFunction=0x00000000, const wchar_t * pszFile=0x00000000, unsigned int nLine=0, unsigned int pReserved=0) Line 112 + 0x7 bytes C++
msvcr90.dll!_invalid_parameter_noinfo() Line 125 + 0xc bytes C++
PAP.exe!sf::Ftp::Download() + 0x39d bytes C++
PAP.exe!receiveFileFtp() Line 37 + 0x3f bytes C++
PAP.exe!FTPserver(std::basic_string,std::allocator > nick="led", std::basic_string,std::allocator > score="3") Line 73 + 0x5 bytes C++
PAP.exe!ScoreBoard(sf::RenderWindow & Window={...}, std::basic_string,std::allocator > nick="led", std::basic_string,std::allocator > score="3") Line 128 + 0x56 bytes C++
PAP.exe!wWinMain(HINSTANCE__ * hInstance=0x00400000, HINSTANCE__ * hPrevInstance=0x00000000, wchar_t * pCmdLine=0x000209e4, int nCmdShow=1) Line 583 + 0x3d bytes C++
PAP.exe!__tmainCRTStartup() Line 578 + 0x1c bytes C
kernel32.dll!7c817077()
[Frames below may be incorrect and/or missing, no symbols loaded for kernel32.dll]

This looks like a checked iterator is barfing on you; do you have the source for the sf::Ftp::Download() function? If so, what is the context in which the crash occurs?

Yes, the code is available at sfml website:
FTP.hpp: http://www.sfml-dev.org/documentation/1.6/Ftp_8hpp-source.htm
FTP.cpp: http://www.sfml-dev.org/documentation/1.6/Ftp_8cpp-source.htm

Here is the relevant code:
(I marked the relevant code with: \\<------)

FTP.cpp
http://pastebin.com/de3uFpYb

ScoreBoard.cpp
http://pastebin.com/xBv1Yrg5

In the call stack, double-click on the frame PAP.exe!sf::Ftp::Download() and see where exactly in the Download() function things are dying.