Could you please provide a bit more detail for us? For example, what is your process to upload the documents? What types of documents are they? PDFs? Word documents? Something else? Are you uploading them to content pages? Are you trying to create links to the documents? Any additional information you might be able to provide would be great...thanks!
In addition to the info @Chris_Hofer asked about, could you also visit the Files area in your course to check your available storage space? There should be a percentage bar at the bottom of the files page indicating how much storage you have used. If you're at or near 100%, that can cause errors when trying to upload new material.