We run a website where we use dynamic "subdomains" to determine/set a few variables within our codebase. The subdomains are not actual domain-entry subdomains, but just that -- dynamic. We validate them in our code and redirect to a homepage if they are invalid.
For example...
I just had this exact same thing happen to me 10 minutes ago!
I have a few boxes running the exact same setup, so I had to copy over the /usr/lib/rpm directory and of course add the symbolic links and finally added rpm to /bin.
This should fix it but I'd still run : yum install rpm-build.x86_64