Solution : https://service.sap.com/sap/support/notes/720083 (SAP Service marketplace login required)
Key words : 
20 basis support package 38 requires sap kernel patch level 1269, system_imode_too_large runtime error occurred, apo-based solutions benefit, service marketplace software center, importing support package kernels, add basis support package 38, importing basis support package 38, create larger internal tables, 20  > binary patches  > sap kernel 6, 20 basis support package 38
Related Notes : 
       
| 782140 | OCS: Known problems with Support Packages in Basis Rel. 6.20 | 
| 548845 | Internal modes uses more than 2 GB | 
| 447925 | OCS: Known problems with Supp. Packages in Basis Rel.6.20 | 
| 211077 | Replacing target release kernel during upgrade/EHPI | 
| 143550 | ST03/workload: User exit for individual processing | 
| 19466 | Downloading SAP kernel patches |