SNAPSHOT TOO OLD (ora-01555) error

I am getting below ORA-01555 in DB13 warnings in CHECKDB logs very often.
                     

Can you investigate the following problem: Abap YWDSR098 is scheduled daily. Since 01/08/2008 the progam is terminated with following error :
                       SQL error 1555 occurred when accessing table "LTAK ".

                       Database error text........ : "ORA-01555: snapshot too old: rollback segment  
                        number 12 with name "PRS_11" too small#"                                    
                       Internal call code........ .: "[RSQL/FTCH/ LTAK ]"                             
                       Please check the entries in the system log (Transaction SM21).               
 
This is temporarily coming and causing short dump ORA-01555 in ST22 because of report YWDSR098 or table LTAK.
 
Rollback tablespace is only 50% free. Table LTAK is computed by scheduling the job.
 
Kindly give any solution so that this temporary warning can be eliminated, pls keep in mind that the Rollback tablespace is 50% free and Table LTAK is being analysed manualy by brconnect.