Problem in drop tablespace

[abdulhameedom]

I WANT TO KNOW IS THIS PROCESS ARE CORRECT FOR DROP A TABLESPACE


startup open;

alter tablespace raja offline;


SQL> DROP TABLESPACE RAJA INCLUDING CONTENTS AND DATAFILES;
DROP TABLESPACE RAJA INCLUDING CONTENTS AND DATAFILES
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-00942: table or view does not exist


THIS IS THE ERROR I FOUND
BUT ONCE I DROP ANOTHER TABLESPACE WHICH IS AUTOMATICALLY GENERATED BY THE ORACLE "SYS_UNDOTS"


SQL> ALTER tablespace SYS_UNDOTS offline;

Tablespace altered.

SQL> DROP TABLESPACE SYS_UNDOTS INCLUDING CONTENTS AND DATAFILES ;

Tablespace dropped.

THE ABOVE IS WORKING BUT I WANT TO DROP A USER TABLESPACE

LET ME KNOW THE REASON FOR THIS DIFFERENCE ?
IS THERE ANY DIFF BETWEEN "SYS_" TABLESPACE AND "USER"(created by dba)

EVEN I CREATE A NEW TABLESPACE, THAT ALSO CANT ABLE TO DROP.. SAME PROBLEM FOR THAT TOO