I would try using EVAL after concatenating your NZ's and your additions signs to make a proper string. Should look like the below;
=EVAL(Nz([List341].Column(0),0) & "+" & Nz([List346].Column(0),0) & "+" & Nz([List929].Column(0),0) & "+" & Nz([List931].Column(0),0))
I'd also rename your Lists...