Merging BEx hierarchy and dimension in WebIntelligence

I want to merge a hierarchy (from BEx) with an XLS file on a dimension [project]. From my XLS file I have [project] , key figures and other dimensions , so I've got key figures by [project] broken down other dimension. When in my WebI report I put only merged object and key figures , with a formula using Descendants() function it is working well, rollup are working. But when I add another object from the XLS file, so it doesn't work any more, some rows displays #ERROR

here is my variable formula= If ([Query 2].[ITEM HIERARCHY].IsLeaf=1) Then [Euro] Else Sum([Euro] ForAll([Cost Element]);Descendants([Query 2].[ITEM HIERARCHY];1;Self_After))