couldn't write anything to one register

What could be the problem if I'm not able to write this value to this register?

*AT91C_EMAC_TCR = 0x30;

If I take a look in the memory window I don't see this value in this register...

assembly-window shows this code for this c-line:

0x100002E4  E3A00030  MOV       R0,#0x00000030
0x100002E8  E2441911  SUB       R1,R4,#0x00044000
0x100002EC  E5810010  STR       R0,[R1,#0x0010]

Looks really good, but it doesn't work... I'm working with the AT91Rm9200 controller from Atmel.

best regards
Johannes