I had the same problem, for me, it turned out to be a function which, for security reasons, is banned on our servers.
If you can’t see images in the file browser, you may want to try this:
Open the following file:
Around line 98 - 100 should be the following bit of code:
Change it to this (providing you can use fopen):
$fp = @fopen($icon,"rb");
That got it working for me.