[CMake] "Can not open file" Problem

[Chunyan Jiang]

Dear Cmake users,
I meet a strange problem. I make project using VC++ 6 under WindowsXP.
I have a project and some classes. For example, MyProject and class A, class B
If I organize files as:
/MyProject/CMakeLists.txt
/MyProject/A.h
/MyProject/sub/B.h

In A.h file, #include "B.h"

Build the project, there is error messages:
Fatel error: can not open B.h or no such file

If I store A.h and B.h in same folder, there is no errors. If I
organize files as:
/MyProject/CMakeLists.txt
/MyProject/B.h
/MyProject/sub/A.h

In A.h file, #include "B.h"

There is also no errors.
In CMakeLists, I just set it as

SET(HEADERS
A.h
sub/B.h
)

There are many example project that use sub folders. No error messages
occur in building. I compared my CMakeLists.txt to them, but I didn't
find the difference.

Could some one tell me how to solve this problem?

Thanks!

Chunyan