The only reference to the error that I could find for Exchange 2013 related to domain controllers not being in the default Domain Controllers OU. Sure enough, this client had added child OUs inside of Domain Controllers. The child OUs were being used to control how WSUS was pushing out updates to the domain controllers.Exception has been thrown by the target of an invocation
To resolve the issue, we moved the domain controller computer objects back directly into the Domain Controllers OU and removed the child OUs from inside the Domain Controllers OU. We did this in all three domains.
A blog article that I used when troubleshooting: