Unfortunately its nothing I can test - hopefully someone else will be able tell me whats wrong...
Here are the headers too :
#ifdef SERIAL_EXPORTS
#define SERIAL_API __declspec(dllexport)
#else
#define SERIAL_API __declspec(dllimport)
#endif
#define MAX_RCV_QUEUE 2000
#define MAX_RSP_SIZE 200
// This class is exported from the Serial.dll
DWORD SERIAL_API Wait(DWORD dwDelay);
DWORD SERIAL_API ReadRsp(DWORD hCOMPort,DWORD store,DWORD storeSize,DWORD errorPtr,DWORD errorSize);
DWORD SERIAL_API WriteCmd(DWORD hCOMPort,LPSTR pchCmd);
void SERIAL_API ClearTxBuff(DWORD hCOMPort);
void SERIAL_API ClearRxBuff(DWORD hCOMPort,DWORD errorPtr,DWORD errorSize);
DWORD SERIAL_API CharsReady(DWORD hCOMPort,DWORD errorPtr,DWORD errorSize);
DWORD SERIAL_API CloseComPort(DWORD hCOMPort);
DWORD SERIAL_API OpenComPort(DWORD nPort,DWORD nBaudRate,DWORD errorPtr,DWORD errorSize);