Kim Kardashian’s sex tape with ex-rapper boyfriend Ray J is at the center of controversy again. Ray J threatened legal action to protect his interest in the tape, which he shares with Kim.

An unknown party is attempting to buy the rights for the video, currently owned by porn purveyor Vivid Entertainment. The buyer wants to take “Kim K Superstar” off the market.

Ray J apparently got wind of the deal and had his lawyer fire off a letter to Vivid Co-Chairman Steve Hirsch, according to gossip site TMZ.

“Any attempts to transfer the copyright outside of these parameters will result in filing a motion with the courts to seen an injunction of any sale until Ray J’s rights are protected,” the letter states.

Kardashian and Ray J were nobodies when they made the sex tape. Four years ago, in February 2007, it suddenly leaked onto the Internet, and Kim became an overnight sensation.

After initially protesting, Kim cut a $5 million distribution deal with Vivid to sell the tape, which has reportedly made millions of dollars. It helped launch her career. She and Ray J get a cut of the profits.

Now the rights to the tape are estimated to be worth $30 million.

Both Ray J and Karashian have complained about how the tape continues to dog them.

“My client rarely has a conversation with industry professionals where the Tape has not been mentioned or questioned,’ the rapper’s lawyer wrote. “No amount of money can relieve him from this nightmare.”

Kim, who recently married NBA star Kris Humphries, says she regretted making it, but where would she be without it?