I use *Windows 7 Professional Edition x64*.

When I take the checksum of a system DLL, such as `%windir%\System32\shell32.dll`, it will differ from the checksum of a copy of that file - that is, taking this file and making a copy of it to another folder. Why?

Additional information: according to `sfc /scannow`, my file `DxpTaskSync.dll` is corrupted. Therefore I replaced it with the original version from the Windows 7 installation CD. Whenever I copy the original version back and forth between the `%windir%\System32\` folder and some other folder, the checksum changes back and forth. For taking the checksum, I use *RapidCRC*. Despite replacing `DxpTaskSync.dll` with the original version, `sfc /scannow` still reports corruption.