error LNK2019: unresolved external symbol problem

[namelessone]

I have written two MFC application in VC++,
now i want to combine them together in VS.net 2003 C++ by adding them
into the same solution. (i.e now i have 1 solution including 3
projects, the master one and other 2 i have written)

in the master project file (LoadMasterDMDlg.cpp), the code is to
create an instance of a CAutoApp object. and I include "\Auto.h" in
this file.

void CLoadMasterDMDlg::OnBnClickedTdatabtn()
{
// TODO: Add your control notification handler code here

CAutoApp app;
app.InitInstance();

}

but the compiler gives me error msg: "LoadMasterDM error LNK2019:
unresolved external symbol "public: virtual int __thiscall
CAutoApp::InitInstance(void)" (?InitInstance@CAutoApp@@UAEHXZ)
referenced in function "public: void __thiscall
CLoadMasterDMDlg::OnBnClickedTdatabtn(void)"
(?OnBnClickedTdatabtn@CLoadMasterDMDlg@@QAEXXZ)"

could anyone tell me what should I do make the instance?