Problem with LoadLevelAdditive Timing

So I have a little problem which seems to me about the timing of LoadLevelAdditive.
I’m instantiating a player object which in its start method instantiates another class that loads some UI from a seperate scene. in the same start method I try to excess that UI, but it is always null. when I output the contents of the UI scene it seems that it is only a valid object in the second update.
how can I solve this?

You can make the Start() function wait one frame before trying to access your variable using a co-routine:

IEnumerator Start(){ // Change the function type from 'void' to 'IEnumerator'
    // Do something...
    yield return null; //Wait one frame, then continue the function
    // Access your variable

Update() cannot be co-routine, but you can use simple boolean logic to skip one frame before trying to access it:

bool canAccess = false;

void Update(){
        // Access your variable
        // Set 'canAccess' to true. The above 'if' statement will run next Update
        canAccess = true;