I would first search for it in the windows folder... you'll find it 3 times in (system32, syswow64 - if you run 64 bit... and deep in another folder. If the file size and date isn't exactly the same 4.50 kb and 7/13 I would copy a good one over the modified one... or extract it from Ie_extra.cab on the install disk and overwrite the modified one(s)
If they do not appear to be corrupt or modified (overwritten by a different version when you installed software -- for example on my system Quick Books Pro has included an older version that may overwirte my Win 7 dll when it installs??)
you may have some kind of abnoral user name. Windows WILL allow user names with spaces.. but then it crokes on many operations that are...