Resolution
When executing a particularly large aggregation, Access Governance Suite may throw an exception due to a timeout error if the aggregation time exceeds the 10 minute threshold. The error message will say: "Exception during aggregation. Reason: java.lang.RuntimeException: Error while iterating. Java.util.concurrent.TimeoutException"
To solve this problem, edit the Configuration:SystemConfiguration (accessible through the Debug Pages, System Configuration option) and increase the smReadTimout value. This entry expects a value in minutes and the default value is 10 minutes.