Current version of XSIBackup does not keep thin provision of disks when copying them over the network with rsync (it does when copying between datastores), so you should make sure you have enough space on the other side to host the files you are copying. In any case there is an easy solution; use vmkfstools to claim the empty space and convert your disk back to a thinned state at the target machine by issuing: vmkfstools --punchzero your-vmdk-file.vmdk
If you do not have room enough to manouver try to delete any file (apart from the .vmx and .vmdk files) and any other file or backup you can remove temporarily. If you are still in trouble consider upgrading to a bigger disk.