Yout ORA-01562 message contains also the exact cause of the error - "ORA-01628" which has the following error message: "max # extents (string) reached for rollback segment string".

This means that your rollback segment has the above limit different that you thought it is - obviously it is not 249 as you think. Either the RB segment or the tablespace it is residing in must have been created with some MAXEXTENTS specification in the storage clause. Check the MAX_EXTENTS in DBA_ROLLBACK_SEGS.

HTH,