Hi Gavin, I tried adding a new CPP file to my project and had only this in the file, #include<boost/unprdered_map.hpp" unordered_map<std::string, std::string> a; That has the same compilation error. I tried both of these, * Create a .i file from it, replace the contents of the cpp by the contents of the .i and compile just that file * Add a new CPP file in my project and put the .i created from the above file as this new files contents Tried compile both the above files only(file only compilation) and I get these errors, ------ Build started: Project: Worker , Configuration: Debug Win32 ------ Compiling... I_File_UMAP.cpp c:\codeworks\i_file_umap.cpp(3407) : error C2011: 'localeinfo_struct' : 'struct' type redefinition c:\program files (x86)\microsoft visual studio 8\vc\include\crtdefs.h(2042) : see declaration of 'localeinfo_struct' c:\codeworks\i_file_umap.cpp(3413) : error C2011: 'tagLC_ID' : 'struct' type redefinition c:\program files (x86)\microsoft visual studio 8\vc\include\crtdefs.h(2048) : see declaration of 'tagLC_ID' c:\codeworks\i_file_umap.cpp(3422) : error C2011: 'threadlocaleinfostruct' : 'struct' type redefinition c:\program files (x86)\microsoft visual studio 8\vc\include\crtdefs.h(2057) : see declaration of 'threadlocaleinfostruct' c:\codeworks\i_file_umap.cpp(4167) : error C2011: 'std::_Lockit' : 'class' type redefinition c:\program files (x86)\microsoft visual studio 8\vc\include\yvals.h(561) : see declaration of 'std::_Lockit' c:\codeworks\i_file_umap.cpp(4314) : error C2011: 'std::_Mutex' : 'class' type redefinition c:\program files (x86)\microsoft visual studio 8\vc\include\yvals.h(708) : see declaration of 'std::_Mutex' c:\codeworks\i_file_umap.cpp(4366) : error C2011: 'std::_Init_locks' : 'class' type redefinition c:\program files (x86)\microsoft visual studio 8\vc\include\yvals.h(760) : see declaration of 'std::_Init_locks' c:\codeworks\i_file_umap.cpp(8913) : error C2011: '_iobuf' : 'struct' type redefinition . . . Worker - 102 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Thanks, Ram