hi,

you should check the RESET and XTAL as well.
From AT89S8252 datasheet:

Both the Code and Data memory arrays can be programmed using the serial SPI bus while RST is pulled to VCC.

and:

Either an external system clock is supplied at pin XTAL1 or a crystal needs to be connected across pins XTAL1 and XTAL2.


Read more details in section "Serial Downloading" from AT89S8252 datasheet

Another datasheet which may you help you alot is AT89S8252 In-System Programming
Regards,
Oleg