You can't share the Windows folder itself, or any system folders inside it. If you need to have those folders shared on the network, you'll have to share the root directory of the C: drive. This will make all files and folders on your C: drive available on the network, but if you need to have the contents of C:\Windows available on the network, it's really the only way I know of to do it.
I assume that you need to copy some files from C:\Windows\SYSTEM32 from one PC to another. If this is the case, just temporarily share the entire C: drive, copy what you need, then delete the share.
Edit: Another option would be to copy the entire contents of the SYSTEM32 folder (or just the files you need) to a different location on your PC--Windows may or may not let you do this depending on whether the files you need are currently in use--and then share that new folder on the network.