How to synch user on the page with items of list displayed on the page

Hello,

So I've been trying something I thought easy but encountered some problems, what I've been doing wrong, here is the situation : 

=> User going on a page to enter some info about themselves in a board (grid). 

They open the page. They have to select their user name, as "Name", because their name in the database is different from their "Anaplan Users" names. 

Here is what I want to do : 

=> User going on the page, the page is automatically synched with their "Name", based on their "Anaplan Users" name.

What I did :

=> Module, with "Users" as a dimension, displayed on the dashboard, while in backend I have a module based on their "Name" (why double-module ? well today lots of calculations depend on this "Name", I don't want to re-write all my formulas for a little change like this). User enter their info in the dashboard based on their "Anaplan User" name. Then I take this info in my backend module thanks to a formula.

(/!\ I don't want to have an import to make, users don't want to click on buttons). 

What my problem is :

=> Every formula I tried gives me the error : "Invalid formula for INPUT_BACKEND_Employees.Value: Automatic sum of INPUT_DASHBOARD_Users.Value over Users hierarchy is not possible as Users does not have a built-in top level" 

But the thing is, I have the same dimensions, I don't need to do any sum for my modules, I don't understand what's going on here. Did someone encountered the same error ? How to fix it ?

Camille.