Press Secretary Robert Gibbs released the following statement:

Senator Gregg reached out to the President and offered his name for Secretary of Commerce. He was very clear throughout the interviewing process that despite past disagreements about policies, he would support, embrace, and move forward with the President’s agenda. Once it became clear after his nomination that Senator Gregg was not going to be supporting some of President Obama’s key economic priorities, it became necessary for Senator Gregg and the Obama administration to part ways. We regret that he has had a change of heart.

Link to White House blog post