This issue comes when you try to install Windows Server 2012 from the downloaded evaluation ISO file. Actually sometimes the installation files get corrupted during the downloading from Microsoft website. To resolve this issue, you can try this :
1. Change your NIS’s DNS to Google : 184.108.40.206
2. Clear DNS cache by running ipconfig/flushdns command
3. Use a different browser to download the installation media again
4. Try to install again
Hope this helps!