Server not rebooting with raid connected

I have a weird problem that I have not encountered before. I have Server 2008 installed on a separate drive with a 4 drive RAID 5 array in the machine. If I reboot the machine, it gets to the OS loading bar and then stalls and never loads windows. If I unplug 1 of the drives in the RAID array, the machine will boot into windows normally and I can then plug the drive back into the RAID array and everything is fine. Does anybody have any ideas why the RAID would be stopping windows from loading? Needless to say, not being able to boot into windows without manual intervention is causing some serious headaches. Thanks in advance for the help.