MFC C++ LINK 2019: unresolved external symbol "public: __thiscall

VC2012, I have a solution with many projects.
I have made a "Common" project that contains classes to be used from another projects (for general purpose).
Under "Common" I added a class named

"PreRequisitesManager" (cpp+h)

and interface

(PreRequisitesInterface).

On "Client" project (Added as dependency the "Common" project) I have class

ClientDlg

. the interface was added as needed and added a member of type

'PreRequisitesManager'

.

The ClientDlg.h includes "PreRequisitesManager.h"
PreRequisitesManager includes the PreRequisitesInterface.h.

I am getting this:

GetCVClientDlg.obj : error LNK2019: unresolved external symbol
"public: __thiscall
CPreRequisitesManager::~CPreRequisitesManager(void)"
(??1CPreRequisitesManager@@QAE@XZ) referenced in function
__unwindfunclet$??0CGetCVClientDlg@@QAE@PAVCWnd@@@Z$0 GetCVClientDlg.obj : error LNK2019: unresolved external symbol
"public: __thiscall
CPreRequisitesManager::CPreRequisitesManager(void)"

(??0CPreRequisitesManager@@QAE@XZ) referenced in function "public:
__thiscall CGetCVClientDlg::CGetCVClientDlg(class CWnd *)" (??0CGetCVClientDlg@@QAE@PAVCWnd@@@Z) .

Answer

Fixed.

the problem was the project was compiled as EXE and not as DLL.

Thanks for help.