Help identifiying this exception

Question

Hello.
I've been working on a project for a while now, that deals with displaying a set of JPGs from a server, then swapping those images with new images, and displaying those. However, I just came across an exception error that I have never got before and have no clue where to start looking. This is exactly what it says:
Java(TM) Plug-in: Version 1.4.2_01
Using JRE version 1.4.2_01 Java HotSpot(TM) Client VM
Uncaught error fetching image:
java.lang.NullPointerException
     at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
     at sun.plugin.net.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
     at sun.awt.image.URLImageSource.getDecoder(Unknown Source)
     at sun.awt.image.InputStreamImageSource.doFetch(Unknown Source)
     at sun.awt.image.ImageFetcher.fetchloop(Unknown Source)
     at sun.awt.image.ImageFetcher.run(Unknown Source)Any ideas? Within the function that loads it and everything, I would call gc() to help my memory managemtn. I first thought that perhaps the gc() was deleting it before it would show it. Yet, I took it out, and it still shows up.
Thanks for ANY help or suggestions on where I could start looking

Answer 1

Ok, so I have an array of images called img[]. I do the following to add an image to the array:
img[i] = getImage(getCodeBase(), images[current_img+i]);
tracker.addImage(img,0);
so, I added a few lines to check if it was null, like you said
if(img[i] != null) {
     g.drawImage(img, 0, 35, this);
Is that what you were referring to, or were you suggesting a different method. And thanks for all the tips guys! Its giving me someplace to start with.