When trying to mount the APIC-EM ISO from the KVM console by mapping it to my computer. There seemed to be an issue with the transport or booting from such a large file multiple hops away from the UCS server I was installing this on (bare metal install). So, I ended up moving the ISO to a server already in the environment I was trying to install APIC-EM in, and mapped it from there. Worked very well and much, much faster. Best practice is to have the install media as close to it's target as possible.
Note: Preseed takes a while. Patience is a good thing.
Also this can because of reasons as mentioned below.
1. installation with corrupted iso. Please check md5 checksum after you download the iso.
2. If the disk is unmounted during the installation process (especially while uploading all the bundles to machine from ISO attached)