Oracle Message ORA-00846 - could not shrink MEMORY_TARGET to specified value

ERRORcould not shrink MEMORY_TARGET to specified value
CAUSEAttempted to shrink MEMORY_TARGET to the specified value but did not succeed because the PGA and SGA components could not be shrunk.
ACTIONDo not set MEMORY_TARGET to a value below the current value without first shrinking the individual memory components.