mfc100d.dll is not located from within system32

Hello,

I have an application that requires the mfc100d.dll.

First I copied it to c:\windows\system32, but the application did not located this dll. Therefore the application failed to start.

Secondly I copied the mfc100d.dll into the directory where the *.exe of my application resides. Now the application started without problems.

For me looks that strange, ....  why was the mfc100d.dll not located, when it was in c:\windows\system32 ???