All Oracle Error CodesOracle DBA Forum

ORA-00383:

DEFAULT cache for blocksize string cannot be reduced to zero
Cause: User attempted to reduce db_cache_size to zero, or attempted to to reduce db_<n>K_cache_size to zero while there were still online tablespaces with blocksize <n>K. Note that since the SYSTEM tablespace cannot be taken offline, it is always illegal to set db_cache_size to zero.
Action: Offline any tablespaces with the corresponding blocksize and then perform the operation again.