I recently had an issue where my Dell PowerEdge 710 was displaying an "iDRAC 6 communication failure"error message and refusing to boot cleanly.
This was really aggravating as it would not clear, even if I removed the physical DRAC card.
Eventually I came across this article which advised changing the Power Recovery policy (under Securty) to "always off". One full power off later, and everything is working as expected!
Silly Dell...