I am having the same problem for 89LPC931 on a PCB with the equivalent ISP circuit to MCB900. I have a logic analyzer connected to the processor lines for ISP. Before programming the device, all blank checks, security bit reads and device signature reads work. The waveforms match the Keil documents on applicable ISP lines. The program is successful the first time and the test application runs correctly. After the programming, I get the "unable to connect ..." message. When I look at the signals on a logic analyzer all the inputs (RXD, RTS, DTR) from the comm port still look good, The "U" is being sent on the data line, but the device is not echoing the character. I have changed out the chip 2 times - same response. I read the programmed devices on the parallel programmer. The boot vector has been changed from 1Eh to 1Fh. This makes the ISP fail on subsequent tries. I can't see anything happening on the power line or reset that seems wrong during the programming.