I had exactly the same problem with my '98 528i from 3 years ago when I bought it. Did the usuals like checking fuses etc, no joy. However, yesterday, in a moment of brilliance I stumbled on a similar thread which also mentioned checking the wiring, so I did. The rubber concertina (sp?) that leaves the car above the boot (trunk) and enters the bootlid contained 3 snapped wires.
£5 later on wire connectors, I now have remote boot opening, a boot internal light, a boot that now opens from the drivers seat button and a big smile on my face!
Thanks very much!
Next job is to get the ABS/DSC light off (ABS sensor on order as old one was very tired looking) and PDC to work. They currently beep for a while when you put the car into reverse but then will happily let you reverse into stuff without so much as a squeak!
Thanks again and keep up the good work!