Presumably you have constructed a custom resource file to display your GUI.
You should check the paths to any picture file, make sure they are correct.
For example:
text = "MyPicture.paa";
If the picture is PBO'ed along with the rest of your pictures and the PBO is put in the Addons folder, that line should read :
text = "Mypbo\MyPicture.paa";
or possibly
text = "\Mypbo\MyPicture.paa";
Planck