Yes, the most likely reasons for difficulties are that it's too long or the site was having temporary problems...
If you're typing them in Word first, you really don't want to go over two pages if you can help it - depending how you're laying it out, of course... You can't really go by the character counter in there, either, as it counts them differently... But two pages/two and a half, or there abouts, is really the maximum the submission box will take... You should be able to see the little counter in the top right corner that starts at 4000 - if it's down to 0, that's fine, but if it's below that by the time you're done typing your piece, it won't go through... So you'll need to trim some, to get the counter back to 0 or above...
If it's a temporary fault, there's nothing you can do except log out and come back another time to try again... There is a huge ammount of traffic on the site now, and people trying to submit at the same time, so errors are unavoidable... But persevere and it should get there eventually - the comp will be open a couple of weeks yet, so there's plenty of time...

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"It's not finished... It's finished..."