C / C++ / MFC

retval = HeapFree(_crtheap, 0, pBlock);
         if (retval == 0)
         {
             errno = _get_errno_from_oserr(GetLastError());
         }

	ntdll.dll!77c90004() 	
 	[Frames below may be incorrect and/or missing, no symbols loaded for ntdll.dll]	
 	ntdll.dll!77d2cad0() 	
 	ntdll.dll!77ce7a57() 	
 	ntdll.dll!77cbb0cd() 	
 	ntdll.dll!77cbafd8() 	
 	ntdll.dll!77caa5a4() 	
 	kernel32.dll!764e3f01() 	
 	kernel32.dll!764e3f01() 	
>	Test.exe!free(void * pBlock=0x3cba86c8)  Line 110	C
 	Test.exe!CMemFile::Free(unsigned char * lpMem=0x3cba86c8)  Line 118 + 0x8 bytes	C++
 	Test.exe!ATL::CStringData::Release()  Line 113	C++
 	Test.exe!ATL::CSimpleStringT<char,0>::operator=(const ATL::CSimpleStringT<char,0> & strSrc="10022*Socket Error")  Line 300	C++
 	Test.exe!CSmtp_Mon_Thread::SmtpResponseThread(ATL::CStringT<char,StrTraitMFC<char,ATL::ChTraitsCRT<char> > > URL_Name="http://dofev.de", unsigned int Port=1018857688)  Line 155 + 0x1d bytes	C++
 	Test.exe!CSmtp_Mon_Thread::OnSmtpTimer(unsigned int idEvent=7843, long dwTime=15468593)  Line 69	C++
 	Test.exe!CWinThread::DispatchThreadMessageEx(tagMSG * pMsg=0x083eb828)  Line 771	C++
 	Test.exe!AfxInternalPreTranslateMessage(tagMSG * pMsg=0x083eb828)  Line 227 + 0xd bytes	C++
 	Test.exe!CWinThread::PreTranslateMessage(tagMSG * pMsg=0x083eb828)  Line 777 + 0x8 bytes	C++
 	Test.exe!AfxPreTranslateMessage(tagMSG * pMsg=0x083eb828)  Line 255	C++
 	Test.exe!AfxInternalPumpMessage()  Line 178 + 0xf bytes	C++
 	Test.exe!CWinThread::Run()  Line 629 + 0x7 bytes	C++
 	Test.exe!_AfxThreadEntry(void * pParam=0x0033eef8)  Line 126	C++
 	Test.exe!_callthreadstartex()  Line 348 + 0x6 bytes	C
 	Test.exe!_threadstartex(void * ptd=0x07e35898)  Line 326 + 0x5 bytes	C
 	kernel32.dll!764eeccb() 	
 	ntdll.dll!77cfd24d() 	
 	ntdll.dll!77cfd45f()