Hi Hasnaa,
Try to declare variable LR_ENTITY as reference of CL_BSP_WD_VALUE_NODE. This is normally used when corresponding context node has some value nodes.
After this, I'm not sure but you can get another kind of error. Don't think you need to get the 'BuilStandardAddressRel' relationship because I think that context node is already pointing to that. So maybe you just need to get the attribute value for 'E_MAILSMT'.
See if it helps you a little more.
Kind regards,
Garcia