The submit button is being hosted on akamai.net, this is commonly blocked in various ad filtering techniques because it is freqently used to host ad images. Blocking it is problematic however, because many sites also use it for legitimate images (such as the submit buttons). To fix the problem permanently, you need to disable or edit anything which might be blocking it (this includes proxies, filtering programs, image permissions, adblock, PAC files, usercontent files, etc). A temporary fix that should work (unless it's your usercontent file that's blocking it) is to turn on image placeholders, then just click where the image -should- be. (You can also move the mouse around the right area until you see "javascript:submit(main)" in the status bar, then click.)
Here's a screenshot:
http://allspark.net/cypherswipe/submit-button.png