Kernel Panic after importing Linux VM

I'm running a VM with Red Hat 5.7 and lastest available LIS drivers installed virtualized on Hyper-V 2008 R2 SP1. 

I'm migrating to Hyper-V 2012 R2 and i've made an export of this VM with success and imported it into the new hypervisor.

When i start the vm, i get an kernel panic error, saying this: 

unable to access resume device (LABEL=SWAP=hda3)

could not find filesystem '/dev/root'  

If i start the vm in Hyper-V 2008 R2, it works like a charm.

Any help will be welcome.