Your problem seems like the one I ran into as well. What I did was double check my COM port in device manager. Opened up matlab and clicked in the "Current Folder" pane, navigated to where I unzipped the "ArduinoIO" package, right clicked the folder and added it and its subdirectories othe path, then execute the "savepath" command.
If that doesnt work, force your COM port to be COM8 or COM5. Also run matlab as admin (SHIFT + Right Click "Run as Adminstrator")