Faults using Storage DRS in vSphere 5

hey there,

i've a small problem using a storage drs cluster in an vsphere 5 environment.

there are 5 datastores in 1 storage cluster (storage drs = on / automation level = manual mode)

in Datastores > "My Storage Cluster" > Storage DRS is the following problem:

Problem: "Could not balance datastore space usage"

Target: "my first esxi host"

under problem details there are a lot of errors like the following one:

Fault: "Storage DRS is disabled on the virtual machine."

Prevented Recommendation: "Migrate VMxy from myfirstesxi.xx.local to any host"

what can i do to fix this fault?

thanks!