If all other files open correctly, I would venture to say you have a corrupted file.
If the Windows Protocol Manager is outdated or has been corrupted by some other application call Windows fails to correctly handle the communication through the network and the calling application. Windows has an updated manager on its download site or you can try to use the system backup copy in windows on your PC and over-copy the bad one with the last good copy.
If you have just installed Excel and are just having this problem it may be a network communication problem?
I would call Microsoft and see what they say! JSW