Credentials (local or AD) can be used to install the agent; yet after the install the agent will use the local system account to establish/maintain communication with the ePO server. Perhaps create a new local or AD account with rights on those systems and try a test deployment.
a small add to tao comment
Distribute again the agent with force option activated to regain control on computers. just add in this task the new credential for that domain. Never try to recover in this sutation the installed agent, just enforce a new one.