Solution : https://service.sap.com/sap/support/notes/514543 (SAP Service marketplace login required)
Key words : 
symptom upgrade/installation plugin 2002, rmcsbwxp_pp_1 xpra program, mcex_update_04 function module, plugin delta-upgrade, plugin delta upgrade, 'generic delta' function, pp extract structures, storing temporary data, generic delta method, lower pi release
Related Notes : 
       
| 701179 | BW-BCT composite SAP note: PI 2004.1 upgrade or SP | 
| 629171 | FI-SL DataSources with delta mode: Plug-in upgrade | 
| 611115 | Composite BW-BCT note: PI 2003.1 upgrade | 
| 587491 | Avoiding unwanted metadata loss | 
| 571592 | XPRA RMCSBWXP_SD_2 terminates during upgrade to PI 2002.1 | 
| 566917 | XPRA RMCSBWXP_IM_01 terminates with error message | 
| 564561 | 2LIS_04_P_MATNR: FA_GLFT field is missing | 
| 554255 | Upgrade to Releases 4.6B/4.6C/4.70 with PI 2002.2 | 
| 554252 | R/3 plug-in: Installation/delta upgrade PI 2002.2 | 
| 543002 | Support for DataSources based on information structures | 
| 534894 | Replication of application components and DataSources to BW | 
| 521685 | No data during text extraction (of items/cons. groups) | 
| 521472 | Plug-In 2002.1| Problems with Appl. 02 extractors | 
| 515537 | Installation/delta upgrade of PI/PI-A 2002.1 | 
| 506694 | Upgrading to SAPI 3.0B | 
| 505700 | LBWE: New update methods as of PI 2002.1 | 
| 458305 | OLTP: System upgrade or SP - What should I be aware of after | 
| 456102 | BW logistics extraction (LBWE): Delta upgrade PI/PI-A 2002.1 | 
| 304379 | Activation errors when installing PI-A 2000_1_ |