In an interview with Howard Stern on Monday, Seth Rogen said Katherine Heigl’s past comments about Knocked Up caught him off-guard. It's not the first time he's been asked about it, and not the first time Hollywood has said Heigl is difficult to work with. However, her remarks are from quite a long time ago. In a 2008 story for Vanity Fair, when asked about it directly, Heigl said that the movie was a "little sexist," and:

...paints the women as shrews, as humorless and uptight, and it paints the men as lovable, goofy, fun-loving guys. It exaggerated the characters, and I had a hard time with it, on some days. I’m playing such a bitch; why is she being such a killjoy? Why is this how you’re portraying women?

Sources: Vanity Fair | Uproxx