Argument is not a com object : null

Question

With ArcEngine 9.3.1 in java (but I suppose, it's the same in .NET), I'm developping an application which loads a mxd file. This file contains about 20 layers with shapefile, JPG's, TIFF's files. This file is located on a remote server but accessible through windows share.

After instantiating a MapBean, I try to access some information on this object but I get an Exception "Argument is not a com object : null".

Here an extract of my code:

//some code initializing the engine

mapBean = new MapBean();  
mapBean.setDocumentFilename("myMXD.mxd");  
add("Center",mapBean); //adding into javax.swing.JComponent

//some Intructions
int count=mapBean.getLayerCount();

//count is 0 but after some time, it becomes the right value !!

So I tried to wait for some thread having finished their jobs in such way:

Thread thread;  
Thread[] threadArray = new Thread[100];  
int threadCount = Thread.enumerate(threadArray);  
for (int threadIndex = 0; threadIndex < threadCount; threadIndex++) 
{  
    try {  
        thread = threadArray[threadIndex];  
        if (thread.getName().startsWith("RetrieveThread")
                || thread.getName().startsWith("Image Fetcher") )  
        {  
            thread.join();  
            threadIndex = 0;  
            threadCount=Thread.enumerate(threadArray);                                  
       }  
            } catch (Exception ex) {  
                ex.printStackTrace();  
            }  
        }

But it doesn't really help.

Has someone an idea how to know when the MapBean is really ready with all his information ?

Thanks in advance,

Fabien