c++ cli - Exception: Cannot marshal 'parameter #X': Pointers cannot reference marshaled structures. Use ByRef instead -

i'm working in vs2010 c++ , have c++/cli call formatmessage() draws strange exception. here block of code below below.

if((m_hglrc = wglcreatecontext(m_hdc)) == null) {     messagebox::show("wglcreatecontext failed");      char* lpbuffer;      formatmessage(         format_message_allocate_buffer|format_message_from_system, // it´s system error         null,                                     // no string formatted needed         ::getlasterror(),                         // hey windows: please explain error!         makelangid(lang_neutral,sublang_default), // in standard language         (lptstr)&lpbuffer,                        // put message here         0,                                        // number of bytes store message         null);      messagebox::show( nullptr, gcnew system::string(lpbuffer), "lastrrror",messageboxbuttons::ok);     //messageboxw(null,(lpctstr)lpbuffer, _t("lastrrror"),mb_ok|mb_iconwarning);          // free buffer.     if(lpbuffer)localfree(lpbuffer);      return 0; } 

i following error @ runtime after messagebox "wglcreatecontext failed" appears.

an unhandled exception of type 'system.runtime.interopservices.marshaldirectiveexception' occurred in spritey.exe   additional information: cannot marshal 'parameter #7': pointers cannot reference marshaled structures.  use byref instead. 

it seems have problem param #7, null in case. param #7 (as far msdn explains) optional , expects valist* inserting format string. i've no use parameter , have therefore input null.

i've seen others who've had problem on forums , online, , theirs have been solved switching version of clr support used \clr:pure regular \clr in project configurations. why make difference?

also has not worked me. can see i'm doing wrong in use of formatmessage()?

thanks in advance,
guy