Can't upload addon

mcu_hq

For some reason, when I try to upload an addon on the addon site I get an empty red box just below the This page is only for adding Vanilla 2 addons

There is no text in the error box and I am trying to narrow down what could be the issue. The PluginInfo array is pretty much the same one I used successfully on that site a few months ago. The size is also below 2MB. Anyone else have the same problem?