RBS and refreshing snapshots

Can someone explain why I got an error saying that rbs 'R02' couldn't be extended while refreshing a snapshot where I specifically asked for rbs 'RLRG'? I've verified that RLRG is ONLINE and nobody else is using it.

Message follows:

begin dbms_snapshot.refresh('CODE','?','rlrg'); end;  

*
ERROR at line 1:

ORA-12008: error in snapshot refresh path
ORA-01562: failed to extend rollback segment (id = 3)
ORA-01628: max # extents (20) reached for rollback segment R02
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 248
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 131
ORA-06512: at line 1

--
Chuck Hamilton
chuckh_at_dvol.com

Never share a foxhole with anyone braver than yourself!