In reply to L'Eeyore:
There is a hidden field on the photo form called 'name' and it should be populated automatically by UKC with your username when the form loads.
There is a function called verify() which runs when you submit the form, this checks that the information in that hidden field is at least 2 characters long. If not is gives the message "Your name field is empty"
My guess is that UKC has a problem putting your username into this hidden field when the form is initially loaded. This is most likely due to the apostrophe in your username - a common problem in many websites where special characters like this have to be escaped.
Someone from the UKC team should be able to fix this very quickly for you, but you cannot really fix it yourself - You could hack around it with a browser explorer / debugger, but that's not a long term solution really.
edit: The photo mods can't fix this for you - Email Alan / the dev team and point them to this thread.
Post edited at 19:28