DS-5 reports "ERROR(TAD11-NAL23)"

After I have enabled MMU, I want to write a value to a specify address by DS-5. The DS-5 reports an error as following:

memory set_typed EL3:0x0000000080006000 (unsigned int) (0x1)
ERROR(TAD11-NAL23):
! Failed to write 4 bytes to address EL3:0x0000000080006000
! Error accessing memory.

Then I read this address by DS-5 again. I find the value has been wrote to the address.

By the way, if I disable MMU, I can write a value to a specify without any error.

What does DS-5 check, after it writes a value to a specify address?

Thanks!