Have you tried the support address yet?
support@blizzard.com
Because I really don't think that any downloadable file is going to help you.
The only thing in my PC is "Checksum.class" its a java utility that is zipped, and compressed for storage.
I am thinking it's part of the original Windows install routines.
It has no accessable location, and can not be copied from the search results to give you.
A quick search at Google comes up with this address, to give you an idea of what I mean, as far as a checksum being some form of data, not a file.
http://www.math.utah.edu/~beebe/software/filehdr/node15.html
Write the support address, they will probably just tell you to do a complete uninstall, with instructions, and then re-install.
One last question, you stated that you, "reinstalled several times on a couple of different computers".
Is there a big honkin scratch on your CD,,, or could it have been left in the sun too long?
Because if it's doing the exact same error on several machines, it sounds like the source disk has problems.