http://sports.espn.go.com/nfl/news/story?id=4491142 The Jets have long wanted a big time WR. They've been mentioned in all of the 'big name' trade talks. I'm sure overtures have been made to Eugene Parker. Might be nothing out of the ordinary, but the Niners are obviously upset at something.
I think they are mostly upset they are screwed out of their first round pick, I know I certainly would be
My guess is that the allegations would be that the Jets spoke with Parker and said or implied they would draft Crabtree in the 1st next year should he go back into the draft. Parker probably mentioned it during negotiations.