Im checking line 1183. It seems to be a bug in 8chan's thumbnail generation process. Possibly the image you are uploading is corrupt or an unidentified format. Please try a different image format and see if it works. In the mean time, I will work on the bug and try to fix it as soon as possible.
When the issue is resolved, I will make a reply noting the bug has been fixed in a >>>/qresearch/ general thread.