The following is from Per Olesen on solutions he found to problems using the MCB900. Thank you to Per for providing this for the benefit of others!
I use the TSSOP types on my boards, so it is not possible to program them in the MCB900, and then move it to the target board.
In 2 cases I had the problem that it would only program 1. Time.
Solution problem 1: I had a RS485 chip on the RxT TxT line on the target board, and with no external power on the target board, the RxT line was overloaded. I simply put a 100K resistor in serial with the input on the 485 chip, and it worked fine.
Solution problem 2: To be safe I had placed a 100uF capasitor on the VDD of the LPC, and it is too much, it kills the rise time of the VDD from the programmer. 22uF works.