You may see the following error in the SharePoint processor log file in Audit and Control Management Server 2013:
Index was out of range. Must be non-negative and less than the size of the collection.
This error may occur when a SharePoint document is currently at version of 0.1 and is checked out by a user. The SharePoint processor throws the above error when trying to process this file, and as a result, ACM is unable to track changes for this file.
To fix this error, apply the update described in this article on the ACM application server: