MB Reader RLW has a guess as to the “occasion” of NY Times bias that led standards editor Allan M. Siegal to complain to both Bill Keller and Arthur Sulzburger, along with a hint for everyone else who’s still speculating:

Judy Miller’s pro-war reporting, if that fits the timeline. That’s the left’s biggest complaint about NYT. The problem should be approached by asking, “What would the left complain about?”