It dont look a problem of Oracle Linux 7. It looks a problem with Anaconda.
Please, search (ex. google) for "error populating transaction after 10 retries failure anaconda Errno 256 No more mirrors to try"
HTH - Antonio NAVARRO
Not much help from the error message. This is tricky to resolve.
The hint is in 'c++'.
By default IIS does not allow double escaping of special characters. There is a setting in IIS to enable 'Allow double escaping'.
So, I don't know how you are installing, but I recommend you dowload the ISO again and try install by a DVD or other media.
Are you installing from a downloaded ISO image? Did you verify the image checksum to verify you had a complete, correct download?
Quirky install problems are usually because of bad media.
Are you sure you are doing the right type of installation and using the right installation media? If you are installing from DVD or mounted iso image (Virtualbox), you need the binary distribution DVD, not the source and not any of the boot images. You should also check the checksums as previously mentioned. You can check my 3rd response at Re: Oracle Linux 6.4 Bootable disk? for more details.