Dear Davido,
BDM physical interface is quite simple, it uses mainly BKGD.
In order to enter BKGD mode you have to have BKGD in 0V and reset the uC.
The problem is that sometimes reset pin is not programmed as that.
The only way to assure this is thru pwr-up reset.
Suggestion from someone who has burned more than 8 EVB BDMs: use 0.1A PPTCs in series with GND(2), BKGD(1), RST(4) and VDD(6 - if you use it). Pullups to VDD from RST and BKGD are nice too.
Cheers,
Celso