That means, phe parameterless constructor must exist, one way or another.
Consider the following:
public class Test1 {
public Test1(string somestring) { }
}
public class Test2<T1> where T1 : new() {
}
Now if I try to define an instance
Test2<Test1> testInstance = new Test2<Test1>();
That would fail with
'App.Test1' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T1' in the generic type or method 'App.Test2<T1>'