I have never seen this error before, it interested my hugely as I didn't think this was actually possible to let happen. Anyway I thought, ok so let's clean the offending OAL up and then I can continue the install.
So I check the Exchange Management Console:
And I check the Exchange Management Shell:
Very strange.. I cannot see the offending OAL anywhere. So I can't delete it nor fix it to continue the setup.
So I fire up ADSIEdit:
Fantastic I can see it. The reason I can see it is because it obviously exists, Exchange wouldn't be complaining about it otherwise, but when looking in the configuration container like I am above I see every object that is held within there, whether it is considered corrupt by Exchange or not.
What appears to have happened is that because the OAL has an issue, that issue being the home server for it doesn't exist anymore, Exchange is not showing it within the EMC or Powershell and thus it isn't fixable from those management tools.
In this instance I knew this was a test OAL and not needed, so I simply deleted it via ADSIEdit (right click, delete).
So can I continue the install now?
You bet, the issue is resolved.
Finally if this is a production environment you could open the object and find the 'offLineABServer' attribute and modify it to a server that does exist in the Org. This should be enough to allow it to show in the EMC or Powershell, where you can then update it and force a rebuild. But if you don't want to do that the above method is safe to use but remember you will have to recreate the object and apply it to databases and/or users ensuring your provisioning engine will be ok with that and continue to reference the newly created OAL with the old.
I hope this helps anyone else that runs into this obscure issue.
Oliver Moazzezi MVP - Exchange Server