Problems that I have had with emulator, only with 87LPC76x series:

The emulator is much more forgiving with regards to initialization.

The 'LPC series have port pins and other functions (Crystal, etc.) that must be initialized to the proper values for the OTP parts to work.

I usually have a SMOKETEST program that includes brief initialization and then toggles a port pin or two. It is easier to check if this is working.