This is a known issue, but only occures during a 20 second window when the first monitored interface of a node receives flows. The NTA Sources resource will show that it is receiving the flows and will have a link to go to that view, but you'll recieve this error. If you wait the 20 seconds, then this issue should not occur and will not occur anymore for this node. We have fixed this issue in the next release that we're currently working on.
This issue appeared in a service pack when we were improving performance by caching the flows before committing them to a database.