Hi,
do a VI client to the vCenter, browse the source Datastore, select the VM/folder that you want to move, right click on the VM/folder and select copy/move as per your convinience. A pop will appear, select the destiniation Daatstore. this should do it.
however following could be an issue:
1. VM's are powered on 4.x host and you are trying to move them to VMFS5 Datastore, as 4.x will not be aware of VMFS5 file system Structure.
try doing a VI Client to vSphere 5 host in case of no availability of VC, but vCenter5 Will be of help in this case.
Or try downloading the Vm's to your local machine using VI client to the ESX hosts, in case Datstores are not shared, once downloaded then again do a VI client this time to vSphere5 host and uplaod the Files.
Regards