Solution : https://service.sap.com/sap/support/notes/704498 (SAP Service marketplace login required)
Key words : 
initial flow context tab add, definition ofgroupware customizing object gwa_custprop, initial flow context, groupware customizing objectscrm 4, terms groupware integration, display->change button, symptom initial download, gwa_stareason failserror message, object gwa_custprop 3, initial download
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