Hi,
Variable you have created are slightly different which i have suggested.You have to use Var 2 in the variable var 3 but you have used Var 1 in this.
use these steps:
Create Var1==Substr(Right([Role];(Length([Role])-Pos([Role];":")));1;3)
Create Var 2==Sum(If [Var 1]="MSS" And [Role_Source]="BW" Then 1 Else 0) In ([User])
Create Var3==Sum(If([Var 2])<>0 And [Role_Source]="ECC" Then 1 Else 0) In ([User])
Apply filter on Var 3 where Var 3 is not equal to 0. No need of to create Var 4.
Regards,
Amit