target machines of project and *.obj are different

Question

I'm compiling a visual c++ project, but get errors:

"1>     2>objd\amd64\BasicFeatures.obj : fatal error LNK1112: module machine type 'X86' conflicts with target machine type 'x64' [D:\xproject\xproject.vcxproj]"

I've checked all items in this thread: https://stackoverflow.com/a/4364020/974101

1. Target machine in Project Property -> Configuration Properties -> Linker -> Advanced is MachineX64 (/MACHINE:X64)

2. Platform in Solution Property -> Configuration Manager is x64.

3. But BasicFeatures.obj's target machine is x86 using "dumpbin /headers BasicFeatures.obj | more":

   Dump of file BasicFeatures.obj
   File Type: COFF OBJECT
   FILE HEADER VALUES
                14C machine (x86)
               1439 number of sections
           52DC8466 time date stamp Mon Jan 20 10:05:26 2014
             230284 file pointer to symbol table
               4F2B number of symbols
                  0 size of optional header
                  0 characteristics
   

4. Executable Directories/Library Directories in VC++ Directories is

   "$(VCInstallDir)bin\x86_amd64;$(VCInstallDir)bin;$(SDK40ToolsPath);$(WindowsSdkDir)bin;$(VSInstallDir)Common7\ide;$(MSBuildToolsPath32);$(FxCopDir);$(PATH);"
   "$(VCInstallDir)lib\amd64;$(VCInstallDir)atlmfc\lib\amd64;$(WindowsSdkDir)lib\x64;"
   

The problem is why the target machine of BasicFeatures.obj is x86 when my project targets x64? And how to change it to x64?

Thanks.