The New York Post has the explanation:
"KEVIN Kline to the rescue. Juilliard's centennial on Monday was supposed to be hosted by Juilliard alumni Christine Baranski and Bradley Whitford. But Baranski is rehearsing "Mame" at the Kennedy Center in D.C. and Whitford is taping his new NBC series, "Studio 60 on the Sunset Strip," in L.A. White knight Kline, who graduated from the school in 1972, will perform a Shakespearean monologue."
"The Juilliard School's centennial gala on April 3 will be broadcast live on the PBS program Live From Lincoln Center, Lincoln Center announced.
The gala will include performances by conductor-composer John Williams, soprano Renée Fleming, actors Christine Baranski and Bradley Whitford, trumpeter Wynton Marsalis, violinist Itzhak Perlman, and pianist Emanuel Ax, as well as remarks by soprano Leontyne Prince.
Baranski and Whitford will perform a scene from Shakespeare's Much Ado About Nothing with an ensemble of Juilliard drama students.
The PBS broadcast will be hosted by soprano Beverly Sills; it will begin at 8 p.m. ET (check local listings)."
First Reporter August 17th
According to the NY Daily News, he will be performing at a gala next April 3rd.