Windows Update App (wuapp.exe) shows 0KB and is not valid

My computer hadn't updated itself in over two weeks and I started getting
suspicious; I went and ran windows update only to receive this error.

C:\Windows\System32\wuapp.exe is not a valid Win32 application.

I went to the folder to discover that the file exists but the file size is
0KB. The date modified is the same as the other files so I'm not sure if it
is a hacked file or not.

I most likely need to replace the file, but I have not found this error
anywhere else on the web, can anyone help me replace the file or fix the
issue?

Thanks,

~Ian
Lincoln, NE
Windows Vista Business 32-Bit