Is there anything required to report to FinCEN to "un-file" a CTR filed in error? Once the corrections are made, a CTR will no longer be required. Thanks!

There is not. I called FinCEN about this several months ago. They said to maintain internal documentation on why the CTR was filed in error and store it with the CTR for audit/exam purposes.

You also might want to conduct training after implementing your corrective action to ensure it doesn't happen again.