You issued the following command：  
ALTER TABLE SCOTT.EMP SHRINK SPACE；  
The SCOTT.EMP table is stored in the DATA1 tablespace that has the following properties：  
DATA1 is a read/write tablespace.  
DATA1 is not autoextensible to an unlimited size.  DATA1 is online.  
Segment space management for the DATA1 tablespace is manual.  
You issued the ALTER TABLE SCOTT.EMP SHRINK SPACE； command that generates the following error：  
ORA-10635： Invalid segment or tablespace type  
 What could be the reason for the failure of the command？（）