The link expression for ITMMASTER, instead of using "ITMREF", have you tried [F:STO]ITMREF? 

Yea, same result.. i think both ways work the same.

The link expression is based on the table key "ITM0" and the joining expression to the header table, which in this case is [F:STO]ITMREF. Using the following is also acceptable [F]ITMREF as during the validation the [F:STO] table will be set as default by the Supervisor. You can verify that the link expression was created correctly by looking at $OUVFIC_LISTE label in the generated source file "WOZSTO.src" in the TRT folder of your endpoint.

Apparently i was missing this declaration in the window management