ORA-01555: snapshot too old: rollback segment number with name “” too small

PL/SQL Developer will remember your most recent windows. If you close the application without closing your windows, it will attempt to authenticate to restart your old sessions. This can become a nuisance if you work in several environments. Try making it habit to close everything before closing the application. You may also try upgrading the application as user21081 suggested.

When you delete data, oracle save delete data because perhaps transaction don't ends with commit and oracle need to restore delete data.

This copy of data is stored in rollback segments. In Oracle settings you have max extends for this segments.

Solution

• You can extend segments
• You can delete data by 'slices':

Sample spliting delete data:

 DELETE FROM table SC
 WHERE SC.evaluationMonth= 'Some month' 
 and SC.evaluationDay= '1';
 COMMIT;

 DELETE FROM table SC
 WHERE SC.evaluationMonth= 'Some month' 
 and SC.evaluationDay= '2';
 COMMIT;

 ...

 DELETE FROM table SC
 WHERE SC.evaluationMonth= 'Some month' 
 and SC.evaluationDay= '31';
 COMMIT;

(you can do a loop, of course )