Solution : https://service.sap.com/sap/support/notes/599134 (SAP Service marketplace login required)
Key words : 
key p_r   = p_r                   seqnr = formula_rows-row_seqnr          binary search, report writer report runtime error message_type_x, complete pointers rrd_ext -> formula_rows, row_formulas     read table rrd_ext, binary search, error message gr214, rrd_ext-type <> 'f', report groups, table rrd_ext, error occurs
Related Notes : 
       
| 392165 | iSeries: Known problems under V5R1M0/V5R2M0 |