Great news, yesterday 2015-05-14, VMware released the patch for the ESXi 6.0 Change Block Tracking (CBT) patch that affected all customers running ESXi 6.0 no matter if you upgraded to ESXi 6.0 or did a fresh install of ESXi 6.0.
The patch will make it possible to backup your virtual machines (VMs) when CBT is turned on. The workaround available before this patch was released included to turn off CBT resulting in longer VM backup job run times. If you turned off CBT for your VMs i guess you can use KB1031873 to turn it back on even though the KB does not list ESXi 6.0.
More information is available in the VMware KB2114076 and i never actually found out what “large number of virtual disks” mentioned in the KB actually means. Was it 4, 8, 16, 32 and so on.
The patch, ESXi 6.0 Build 2715440, can be downloaded via the already mentioned KB or via this link and use either vSphere Update Manager (VUM) or the ESXi host command “esxcli software vib” to install the patch. A reboot of the ESXi host is necessary.