One of the potential deals being discussed--a complicated process called an enrollment corrections resolution--would allow anti-abortion Dems to vote on legislation that would amend the health care bill after it passes. Pro-choice Democrats are not on board with that proposal, and are also threatening to pull their support for reform if Stupak so much as gets a vote on the resolution--whether or not it passes.
It's unclear why, exactly, Stupak postponed his press conference, but a keyed in aide suggests Stupak was planning to announce a tentative deal with leadership this morning, and has likely postponed in order to renegotiate. Another aide says it looks like Stupak isn't gonna get his way...or at least not get everything he wants. More information as we get it. But as always, as major legislation approaches its final vote, things move very swiftly.