Hi Steve, try with the following steps:
1. Open the folder "C:\Program Files\GNU ARM Eclipse\OpenOCD\0.9.0-201505190955\scripts\board"
2. Edit the file "stm32f4discovery.cfg" in a text editor.
3. Change the next line
source [find interface/stlink-v2.cfg]
to
source [find interface/stlink-v2-1.cfg]
4. Restart Matlab, open the simulink model and Deploy to Hardware.