Solution : https://service.sap.com/sap/support/notes/742674 (SAP Service marketplace login required)
Key words : 
\usr\sap\j2e\jc00\j2ee\cluster\server0\log, <port>/sap/monitoring/systeminfoand log, terms web dynpro error solution, expand nodes server->services, default trace file defaulttrace, log controllers tree, web dynpro runtime, detailed version number, provide thefull number, web dynpro problem
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