Have you checked if your Upload Quota is full?
To do this click on the profile button at the bottom of one of your posts. On the right hand side under occupation and interests there's a bar showing how much upload space you've used/have left.
Click on the User Attachement Control Panel link under that and it will bring up a list of all the attachments you've posted so you can delete some of the older ones and free up some space.
Hope that makes sense.
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