We are receiving this error when trying to bulk export about 1300 contacts from CC using the V1 .NET API.
The customer with the error has the new UI in Constant Contact. No activity for the export shows up on the Activity page in Constant Contact.
The message is returned when calling Utility.getActivityDetails(). The message is:
1 0com.roving.RovingServerException: Unexpected RuntimeException in ListReadApiServiceImpl.findSubscriberDetailByList. User Data: findSubscriberDetailByList
My dev Constant Contact account still has the old UI and no issues.
The error you're running into is a performance issue on our side with our new Contacts Management system. At times, it will cause a timeout when trying to import the Contacts and only partially process the import job. This can vary greatly and almost always has to do with load on our servers at the time and not the job in question (I.E. not the number of Contacts, this is as likely to happen with 100 contacts as with 20,000).
We are actively working on multiple solutions for this problem including performance enhancements and code refactoring. At this time, I do not have more of an update on timing on a fix for this than this. Will update when we have more information to provide.