Solution : https://service.sap.com/sap/support/notes/1594611 (SAP Service marketplace login required)
Key words : 
ehp <number>sps<number>-> support package stack guideupdate procedure log, /instguides-> installation & upgrade guides-> sap netweaver-> sap netweaver 7, support packages stack guide, -> maintenance-> sps <number>, corrupted attribute meta data, recreated function module trex_ext_load_history, installation script 'install, fix program errors, existing bwa720 instance, mfdownload procedurefor details
Related Notes : 
       
| 1594554 | BWA 7.20: Meta data corruption for sparse attributes | 
| 1591363 | Function module TREX_EXT_LOAD_HISTORY | 
| 1564568 | BWA monitor: Incorrect check for BWA overload | 
| 1393505 | BWA 7.20: Central Note | 
| 1392570 | BWA 7.20: Installation | 
| 1392526 | BWA 7.20: Update | 
| 1021236 | Linux: Using SAP Kernel 7.01 and higher on RHEL4 and SLES9 |