If MEMORY_TARGET is set to a non-zero value:
- If SGA_TARGET and PGA_AGGREGATE_TARGET are set, they will be considered the minimum values for the sizes of SGA and the PGA respectively. MEMORY_TARGET values can range from SGA_TARGET + PGA_AGGREGATE_TARGET to MEMORY_MAX_TARGET.
Now check if your memory_target is set.
Read this metalink note as well:
The reason why I by mistake posts duplicate posts that in specific network environment,
my posts were not reflected to the forum. I am investigating about that.