Have a look at the PHP upload limits on shared hosting chart for Shared Hosting. I don't know if you are on Shared Hosting or if you are saying that you were previously able to upload files greater than 2GB? I also am not terrible familiar with DOCman and the ability within. With the information given I can say where the issue is, it may even be a traffic limit issue? Perhaps it is time to move to a more robust hosting plan that gives you more control. If you are using Joomla and DOCman as some kind of repository or archive and often have files greater than 2GB to be uploaded and downloaded you require either VPS or Dedicated Server hosting? I hope that helps?
...turns out that my two cents is worth less or more depending on the current exchange rate.
roy darling *my posts seem a lot shorter in my head