"cannot open port!" in a DLL project - c

Question

I made a C Console Application in Visual Studio in order to access one of the COM ports with the following code and all went well.
#include <windows.h>
#include <stdio.h>
#include <conio.h>
/*DWORD dwBytesWrite = 25;
WriteFile(hSerial, "LOOOOOL", n, &dwBytesWrite, NULL);*/
/*
int main(void)
{
int n = 25;
char szBuff[25 + 1] = { 0 };
HANDLE hSerial;
DCB dcbSerialParams = { 0 };
COMMTIMEOUTS timeouts = { 0 };
DWORD dwBytesRead = 25;
dcbSerialParams.DCBlength = sizeof(DCB);
hSerial = CreateFile("COM6",
GENERIC_READ | GENERIC_WRITE,
0,
0,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
0);
if (hSerial == INVALID_HANDLE_VALUE)
{
if (GetLastError() == ERROR_FILE_NOT_FOUND)
{
puts("cannot open port!");
return;
}
puts("invalid handle value!");
return;
}
if (!GetCommState(hSerial, &dcbSerialParams))
{
puts("error getting state");
return;
}
dcbSerialParams.BaudRate = CBR_9600;
dcbSerialParams.ByteSize = 8;
dcbSerialParams.StopBits = ONESTOPBIT;
dcbSerialParams.Parity = NOPARITY;
if (!SetCommState(hSerial, &dcbSerialParams))
{
puts("error setting port state");
return;
}
timeouts.ReadIntervalTimeout = 30;
timeouts.ReadTotalTimeoutMultiplier = 100;
timeouts.ReadTotalTimeoutConstant = 100;
if (!SetCommTimeouts(hSerial, &timeouts))
{
puts("timeouts setting fail!");
}
while (1){
if (!ReadFile(hSerial, szBuff, n, &dwBytesRead, NULL)){
puts("serial read error fail!");
return;
}
else
{
printf("%s\n", szBuff);
}
}
getchar();
return 0;
}
Now I needed to make a DLL project and it gave me the following error: "cannot open port!"
Any idea why?
Thanks