"filelistabsolute.txt" is a file that Visual studio generates and it contains the list of files built in the current build and in prior builds, and is used during a Clean and Rebuild to figure out which files to delete.
It is not used by your application, and has absolutely nothing to do with an
object reference not set to an instance of an object
exception.
The reason you are getting that is that some variable contains null (or a property / method returns null) and you are not checking it prior to using it:
string myString = null;
string newString = myString.Substring(5);
Will cause the problem for example.
Unfortunately, we can't tell you exactly what is null: we can't see your screen, access your HDD, or read your mind.
Fortunately, you have all the tools you need to find it yourself: use the debugger. when you application hits the error, execution will stop, and the debugger will show the line of code that failed. Examine it by hovering the mouse over the variables, and see what is null. Then you can look back through your code to find out why it is null.
Sorry, but that's as much help as we can give, without running your code here!