I just tried myself and it works now, I have successfully uploaded my documents as well. Yeah I suspect that all is requires is just some time for ARRIMA to sync up with our files before we are able to begin the submission process.
I paid two days ago, I am not sure I'm inclined to wait a little longer, perhaps it takes awhile for ARRIMA to be in sync with our files or something. I will keep trying to upload it and if it still doesn't work by Monday I will give them a call.