error occurred when downloading in ML310 board: OPB ERR red light - microblaze EDK tutorial

One problem when i practice the EDK tutorial .....and download the bitstream into ML310..... Using Base system builder,I think the platform define, netlist generation, implementation, software (TestApp.c - LED flash) compilation are all okay. (No error found)

But when I (for the first time --: ) download (in XPS), I found the problems below

1. In hyperterminal,

- I see the message "DDR_SDRAM_32M*64 Running 32bit Test"

and then it is stuck

1. In ML310 board, i see the both of LEDs "OPB_ERR" and "PLB_ERR" are red !! (Meanwhile, the LED "DBG 3" is only green, other "DBG" LED does not flash.

If someone knows what kind of problem this is.....could tell me what is the problem.....