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.
Offline any tablespaces with the corresponding blocksize and then perform the operation again.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e0.htm
https://community.oracle.com/message/830828
https://community.oracle.com/message/1201711
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