No, as 4Sword said, it's because there is so much stuff uploaded to the server it is now full. When the server is full, nothing more can be uploaded. It doesn't have to do with attachment space or anything... 5000 MB is the space allotted on the server, and 5000 MB is how much stuff is on the server. That simple.
In lamens terms, the server is full.
That basically it?