Try delete file " error caused by file"

Hi,

I  migrate a VM, but some file continue in the DataStorage origin. I try to move and deleted this files but I recive this message

Error caused by File /vmfs/volumes/4f.../VM/VM-flat.vmdk

the files are:

vm-flat
vm-delta

I have vSphere 5

I need move or delete this files because I need space for can power ON my vCenter

I tried to deleted this files with rm -f but the message is that this file are in use.

Any Idea??

thanks