Hi abeAZ, and welcome to the VMware Communities!
It seems that the virtual machine couldn't read your installation media. If you created the VM from a copy of Install OS X Mountain Lion.app, it might mean that the application itself contains a corrupt installation image. If you manually attached a disk image, check that it is "connected" -- in Virtual Machine> Settings> CD/DVD (SCSI), verify that the slide-switch is set to ON.
If you'd like more help understanding the problem, find the file named vmware.log inside the virtual machine bundle (here's how) and attach it to your reply.
Cheers,
--
Darius