If you can look at the apache and php error logs and report what is going on that would be helpful.

In Concrete 5.5 (I'm not sure about 5.6) there is a condition in the image processing code where errors or exceptions can be swallowed. It's unlikely given your small image size, but if your per-process memory limit is really low you can run out of memory in the routine that generates thumbnails and crash your process, without anything being reported to the logs. Try something like memory_limit = 64M in your php.ini.

I updated this in my WHM and it FINALLY worked! It was set to 32MB.