Hi Scott,
The MON08 is using internal flash and RAM whereas the MMDS is using external RAM to store and execute the software.
Emulation vs. Monitor Mode.
About the configuration, I suggest you check your oscillator configuration to see how it's configured on MMDS and compare.
On the MON08 in the target application, can you communicate with the MCU via MON08 or it is just playing dead ?
Do you respect the Vdd rise time minimum speed on your board ?
Can you see your reset vector programmed at $FFFE-FFFF ?
Here are few ideas.
Alvin.