matlab2013a and xilinx 14.1 path setting

hello i installed matlab 2013a and have xilinx 14.1. I'm trying to set my matlab path to the xilinx. Xilinx design suite--> system generator-->matlab 2013a. When i did thid i'm getting a error saying FAILED TO RENAME mymatlab/toolbox/local/classpath.txt to mymatlab/toolbox/local/classpath.txt.old permission denied. what do i do plz help