error running sp from SL EXECUTE permission was denied on the object 'spname'

Hi,

I created an stored procedure for one screen custom with vs tools for Dynamics SL. The screen has a button, the when the user click in the button the application execute a stored procedure.

I used call sql for execute the stored procedure. If I do login with SYSADMIN the stored works fine, but the another users get the error "EXECUTE permission was denied on the object ". 

The stored procedure has permission to the MSDynamicsSL and for the user [E8F575915A2E4897A517779C0DD7CE] because the sp has the instruction WITH EXECUTE AS 'E8F575915A2E4897A517779C0DD7CE'

Which other permission is missing?

Thanks,

Mary