VMware ESXi 6.0 has a critical bug in its CBT, that may result inconsistent virtual machine backups.
VMware has just released a new patch thats fixes this:
I have recommended my customer to reset the CBT on there VMs, they can use the script from this link:
Veeam has tested and found that it is necessary to do the CBT reset.
Before Doing a CBT reset, make sure there are no snapshots on the VMs.