problems with serial communication

I'm trying to perform a serial communication with Matlab and a dspic using COM6 port of my pc. I use the following commands: s=serial('COM6','BaudRate',9600); fopen(s); and then I open the serial port, but when I go on Tera Terminal and try to open the serial port, it said that it cannot open the port because it is being used by another application, perhaps Matlab. But why, for me COM6 port should be opened by both of programs. When I disconnect COM6 port and perform a virtual serial port using another program(VSPE), it works pretty well.