Is the protocol select jumper set for TTL or RS232?

If it's setup for RS232 then you should be able to talk to it with the Matrix uProject software. If not, check your comms wiring.

If it's setup for TTL then you should be able to use the PIC with inverted serial.

Have you tried resetting it to factory defaults? Might not be a bad idea just so you know it's at a specific baud rate.

Do you have a common ground between the LCD & PIC power supplys?