access denied on OD 6.1

CRB

i installed OD admin 6.1 on w2k3, and i added all the servers that we are using for deployments. all of them are OD 5.6 SP5, the admin is the only 6.1. so when i go to user access to assgin some deployments from a sender box to a user, it says "The request to view usernames in role was denied. "

i thought that OD 6.1 could work with OD 5.6 sp5?
in the other hand, when i go to deployments on od 6.1 and view deployments, and choose the same sender, i can see all the deployment that it sent today...

so anybody can guess what am i missing here? or do i have to upgrade the sender to 6.1 before i try anything?