This was published as a VMware Knowledge Base article #2030526 here.

In short, you will face this situation if you Virtual Machine configuration is really really old, in which case, the adapter type of the VMDK is set to LegacyESX.

vSphere Replication simply does not recognize that adapter type, and we need to change it by modifying the VMDK descriptor and change it to something modern like “lsilogic”.

I wrote a little script to go through all the VMDKs available and find out if any of them have that adapter type, you can easily modify it to also do a search and replace instead of just search, but I will leave that as an exercise for the reader :)

find_legacy.sh

#!/bin/bash
#
for i in `grep vmx /etc/vmware/hostd/vmInventory.xml | 
   sed -e 's/<vmxCfgPath>//g' | 
   sed -e 's/<\/vmxCfgPath>//g' | 
   sed -e 's/ \//g' cut -d '/' -f 1-5 
do 
  cd $i
  grep vmdk *vmx | cut -d ' ' -f 3 | xargs grep legacyESX
done