Strange LNK2001 linker error - c++

Question

Yesterday I got this linker error. I have searched on google and msdn without success.
My problem:
I have moved some parts of my cpp project in a extern static library. I added the h file to my main project and added the dependencies to the lib files. Unfortunately I get a lot linker errors.
1>Compressor.obj : error LNK2001: unresolved external symbol "public: bool __thiscall NWindows::NFile::NFind::CFileInfo::Find(unsigned short const *)" (?Find#CFileInfo#NFind#NFile#NWindows##QAE_NPBG#Z)
1>Compressor.obj : error LNK2001: unresolved external symbol "public: class NWindows::NCOM::CPropVariant & __thiscall NWindows::NCOM::CPropVariant::operator=(unsigned short const *)" (??4CPropVariant#NCOM#NWindows##QAEAAV012#PBG#Z)
1>Compressor.obj : error LNK2001: unresolved external symbol "public: bool __thiscall CInFileStream::Open(unsigned short const *)" (?Open#CInFileStream##QAE_NPBG#Z)
1>Compressor.obj : error LNK2001: unresolved external symbol "public: bool __thiscall NWindows::NFile::NIO::COutFile::Create(unsigned short const *,bool)" (?Create#COutFile#NIO#NFile#NWindows##QAE_NPBG_N#Z)
1>Compressor.obj : error LNK2001: unresolved external symbol "void __cdecl ConvertUInt32ToString(unsigned int,unsigned short *)" (?ConvertUInt32ToString##YAXIPAG#Z)
1>Compressor.obj : error LNK2001: unresolved external symbol "public: bool __thiscall NWindows::NDLL::CLibrary::Load(unsigned short const *)" (?Load#CLibrary#NDLL#NWindows##QAE_NPBG#Z)
All this methods a part of my extern lib. I have tries a lot of compiler settings without success.
Further more when I remove the lib dependencie completely from the linker I get 26 LNK2001 error. So the linker finds only "parts" of the lib.
Do I use a wrong compiler / linker option for my projects?
edit:
The problem was the parameter define LPCTSTR of the method CLibrary::Load(LPCTSTR fileName). In my lib I set the option "Treat wchar_t as build-in type (Properties->C/C++->Lanuage-> ... ) to No. And now it works.

Answer 1

There's not enough information in the question so my answer merely serves as a guide.
Take one function, for instance bool NWindows::NFile::NFind::CFileInfo::Find(unsigned short const *) and find definition of it in your code. Is it there? With this exact function signature? Is it in unnamed namespace? Is it declared static in source file?
Also, try full rebuild of everything. You'd be surprised how many times full rebuild makes mysterious problems go away.