svMotion fails on specific datastore?

Hi , I have two hosts and each have multiple VMs , so when i want to migrate VMs from one to another some VMs which reside on my Datastore01 return an error of "cannot relocate /path/vmfs" , they cannot be cloned either. other VMs[on  same host] are OK to migrate but these specific ones that are on Datastore01 are erroneous . Datastore01 is working fine (all VMs on it are doing their task just fine and are servicing ) . what could be my problem ? tnx