Are you sure you have chosen the sidebar for the right architecture? If you use the x64 (64bit) version of Windows Server 2008, make sure you downloaded and unpacked the 64bit version of the sidebar to C:Program Files. You can use the x86 (32bit) version of the sidebar in a 64bit version of Windows too, but then you have to install the 32bit sidebar into the folder C:Program Files (x86).
Hope this helps! 😉