Default Domain Policy Corrupted

It appears that our domain's default domain policy is corrupted. The GPT.ini file is corrupted. When I go to open it, I get an access denied error. I tried to take ownership through explorer, takeown, and CACLS with no luck. I also tried DCGPOFIX /target:Domain which froze when the process started. Any thoughts would be greatly appreciated. I have a backup of the GPO but of course when I try to restore it is locks up GPMC.

From the comments, it sounds like you're going to have to boot a domain controller in Directory Services Restore Mode to be able to delete this file. If you've forgotten the password to do so, here's how to reset it.

Even with a corrupted security descriptor, takeown or GUI should allow you to re-claim onwership then permissions. I would suspected file system or disk corruption if it's only on one DC. But since you see access denied on all DCs, please check if you are indeed using domain admin credential - I know it sounds very basic and you might feel offended - but that's the only other thing I can think of. A corrupt security descriptor or file lock doesn't get replicated cross machines.