I need to create a tablespace with non standard block size, (16K)

But when I try to set db_16k_cache_size parameter, I get following
error. I tried smaller values also, but still the same error...

Which all parameters I need to consider while using non standard block size..

I am using O9iR2 WinXP 512MB RAM

db_cache_size 25165824
db_block_size 8192

SQL> alter system set db_16k_cache_size=12M;
alter system set db_16k_cache_size=12M
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-00384: Insufficient memory to grow cache

SQL> show sga

Total System Global Area  135338868 bytes
Fixed Size                   453492 bytes
Variable Size             109051904 bytes
Database Buffers           25165824 bytes
Redo Buffers                 667648 bytes