Q:

linq expression cannot contain lamba expressions exception

var app = (from p in Totali
    select p.TotalImponibile).ToString();

I tried to look on the internet, but I didn't find any solution. 
It's just a select statement. 
In the debugger I get "Expression cannot contain lambda expressions", and in my textbox I don't get any result
some more code in the same method
var app = (from p in Totali
    select p.TotalImponibile).ToString();

string app2 = (from p in Totali
    select p.TotalImponibile + p.TotaleIva).ToString();

txtPrezzoTotale. Text = (from p in Totali
    select p.TotalImponibile).ToString();

A:

Make sure you have the result before calling any method like ToString(). 
var totalImponibile = (from p in Totali
                      select p.TotalImponibile).FirstOrDefault();

if (totalImponibile ! = null)
{
   // now you can use safely..
   string result = totalImponibile. ToString();
}

