Hi Seam,
I had some problems with nonvolatile memories. Try to insert a bigger delay between two write cicles (something like 1 milisecond, only for testing purposes. If it helps, try reducing it). You can insert a routine like:

mov r7,#ffH
djnz r7,$
move r7,#ffh
djnzr7,$

It'll take bout 1ms

Other thing I used to do is to write AAh in the whole memory, check it, write 55h and chec it agan. This could be helpfull to detect bad addressing.

Good luck!