A brief list: Facebook made changes to its gaming platform that hampered Zynga regulars. A critical new game, the Ville, was delayed. Another new game, Mafia Wars II, just was not very good, executives conceded. The heavily hyped Draw Something, acquired in March, proved more fad than enduring classic. Some old standbys also lost some appeal.

“Facebook made a number of changes in the quarter,” John Schappert, chief operating officer, said in a conference call with analysts. “These changes favored new games. Our users did not remain as engaged and did not come back as often.”

Revenue for the second quarter was $332 million, below analysts’ expectations of $343 million. And the company lost $22.8 million, or 3 cents a share in the quarter, although excluding one-time items it had a profit of 1 cent a share — still below expectations.

But the real problem was that Zynga slashed the forecast for its bookings — revenue less fees it pays Facebook — to as low as $1.15 billion for 2012, from $1.47 billion.

It was a somewhat contentious conference call. One analyst, Richard Greenfield of BTIG, brought up to Mark Pincus, Zynga’s chief executive, that he had sold stock at $12 a share shortly after the public offering. Mr. Pincus did not directly respond beyond saying “we believe in the opportunity for social gaming and play to be a mass-market activity, as it is already becoming.”