A Problem when I edit and save the m file with Matlab 2013a

I can not save the m file after I edit the m-file with Matlab 2013a. Note that another process are using this m-file. By check with one Third-party software,I found there are four matlab.exe processes occupying the m-file.By the way my computer is quard-core PC. However this problem did not happen in my Dual-core notebook computer. And It is normal for the quard-core PC with one early version matlab 2012b.