构建失败。错误 LNK2001：无法解析的外部符号

Question

关于错误可能来自哪里有什么想法吗？当我构建解决方案时，我收到此构建失败消息。我有一个 MyFolder 程序文件夹，我复制并粘贴了该文件夹并将其命名为 MyFolder2（现在有两个不同的文件夹用于两个程序：MyFolder 和 MyFolder2）。我还进行了查找/替换，将文件夹中所有文件中的所有“MyFolder”替换为“MyFolder2”，并尽力确保区分大小写。 MyFolder 编译得很好。 MyFolder2 产生以下消息：

1>------ Build started: Project: MyFolder2, Configuration: Release x64 ------
1>Build started 2/15/2012 8:46:34 PM.
1>InitializeBuildStatus:
1>  Touching "x64\Release\MyFolder2.unsuccessfulbuild".
1>ClCompile:
1>  All outputs are up-to-date.
1>  All outputs are up-to-date.
1>  All outputs are up-to-date.

1>Link:
1>     Creating library x64\Release\Homework_dlls\MyFolder2.lib and object x64   
\Release\Homework_dlls\MyFolder2.exp
1>MyFolder.obj : error LNK2001: unresolved external symbol "public: static class     
std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >      
MyFolder2::m_HomeworkType" (?m_HomeworkType@MyFolder2@@2V?$basic_string@DU
?$char_traits@D@std@@V?    $allocator@D@2@@std@@A)

1>x64\Release\Homework_dlls\MyFolder2.dll : fatal error LNK1120: 1 unresolved externals
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:01.09
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========