Thanks Mahadevan, that seemed to sort it. Much appreciated!

Thanks David, I looked at that and it refers to line 31 of some MFC file. When i press retry on the debug assertation window it refers to getAfxAppName() at line 31 of that file with a yellow arrow in the call stack window. Also in the call stack window is a green arrow referring to line 22 of the code that i posted which is the 'CInternetSession InternetSession;' declaration, and refers to a $E4() method. There is also a window that comes up showing an 'Unhandled Exception' which i'm guessing is what the $E4() is. Any ideas on what to do with this exception?

Hey people, I'm developing an application that gets SMS's from a GSM modem and uploads them to a DB. To do this i'm using a CInternetSession object. The app compiles OK but I get a Debug Assertation Error!. I think it has something to do with the internet session object because if I comment out anything to to with the CInternetSession then i don't get the debug error. Infact, simply the 'CInternetSession InternetSession;' declaration at the beginning causes the error alone. Here's the code. sorry about the spaghetti style code - i'm a bit of a newbie to C++ #include <stdio.h> #include <afxinet.h> //#include "StdAfx.h" #include "Serial.h" #define EVER ;; //my thread functions static DWORD listenThread_id; static DWORD WINAPI listenThread(LPVOID ref); char * command = "AT+CMGR=3\n"; char * delcommand = "AT+CMGD=1\n"; int count = 0; bool appRunning; bool sendComm, delComm, sendToDB = false; CString st; CInternetSession InternetSession; void main() { appRunning = true; printf("Application Started. Press q to Quit. \n\n"); printf("Please enter a command. \n\n"); printf("Press r to read\n\n"); if (CreateThread(NULL, 0, listenThread, NULL, 0, &listenThread_id) == NULL) { exit(-1); } while (appRunning) { char inChar = getchar(); if (inChar == 'q') appRunning = false; if (inChar == 'r') sendComm = true; if (inChar == 's') sendToDB = true; if (inChar == 'd') delComm = true; } } static DWORD WINAPI listenThread(LPVOID ref) { CSerial Serial; int port=1, baud=115200; char lpBuffer[100]; if (Serial.Open(port, baud)) { for (EVER) { if (sendComm) { int commLength = strlen(command); Serial.SendData(command, commLength); sendComm=false; } if (delComm) { int commLength = strlen(delcommand); Serial.SendData(delcommand, commLength); delComm=false; } while (Serial.ReadDataWaiting() > 0) { int nBytesRead = Serial.ReadData(lpBuffer, 100); for (int i=0; i<nBytesRead; i++) { printf("%c", lpBuffer[i]); st += lpBuffer[i]; int newMsg = st.Find("+CMTI: \"SM\","); if (newMsg != -1) // Message rec'd { count++; if (count == 2 && lpBuffer[i] != '1') // then the index has been added to the string st { switch(lpBuffer[i]) { case '2': command = "AT+CMGR=2\n"; delcommand = "AT+CMGD=2\n"; break; case '3': command = "AT+CMGR=3\n";