To download program into FLASH, you need to configure H-JTAG and H-Flasher properly.
1 - In H-JTAG, enable Flasher -> Auto download
2 - In H-Flasher, select LPC2129 in the flash list;
3 - In keil, disable the use of flash loader.
Please try again as follows:
1 - Ensure that your program is located in the flash address range.
2 - In H-Jtag, enable the auto download option;
3 - In H-Flasher, select the right chip and don't perform any other operations.
4 - In Keil, please choose download app at startup and uncheck run to main
also try to debug the program in the keil simulator and see if it works or throws the same error while debugging on simulator,..........