Was one a local machine user and the other a domain user?

I'm betting there's something different about the permissions for those two users. Even when you drop two users into the Administrators group, if one of them is a domain user, it inherits a bunch of permissions, some of which might still bork the installer.

A smart installer program would have checked for those things, before starting. A less smart installer program would have gone ahead and tried to install, but checked the return codes for all of the functions it called and put up an error when the functions didn't succeed. The least smart kind of installer would have done none of the above, clearly that's what you got.